For The most part, Illusionist has been swallowed by the modern bard, who is rather quite popular right now.
So. Ymmv.
Oh, those are fighting words. So what you're saying is that the illusionist might suck, but the bard sw....
Um.
Anyway, I have repeatedly discussed my undying love of the 1e AD&D illusionist. I have also said that it isn't entirely rational, but largely based on an illustration in the original
Rogue's Gallery (that illustration and irrational love, by the way, is what led to me series of
One Piece Of Art threads).
Others have mentioned the issue of table variation re: illusions as a reason that the class wasn't that popular. But there is a much more fundamental reason. The class was practically designed to fail.
Let's start with the basics. The illusionist was a subclass of MU. Now, most of the subclasses were either more powerful (Paladin, Ranger) or at least arguably better and different (Druid, Assassin) than the prime class. But illusionist? As detailed below... NO.
First problem- the stats.
But to be a MU, you had to have a ... wait for it ... 9 intelligence or higher. (No, there was no "minimum" dexterity, because if you havd a 5 or lower you could only be a cleric, which is one of those weird things I covered elsewhere). And if you had a 16 or higher intelligence, you had a 10% bonus to your XP!
To be an illusionist, you had to have a minimum 15 intelligence AND a minimum
16 dexterity. Moreover, unlike the MU, you didn't get any bonus to your XP!
So right from the start, you see the problem. If you rolled a 16 or higher intelligence, and you didn't choose a MU, you were leaving that sweet XP bonus on the table. Admittedly, there was an arguable case for the person who rolled the 15 intelligence.
Which brings us to the dexterity requirement. 16!!!! Just think for a second... First, there are other classes that absolutely needed that. Thief? Assassin? Monk (minimum 15)? In addition, none of the fighter classes needed it, but they sure wouldn't mind having the AC bonus and the advantage for ranged combat! You would be putting an amazing stat, that gave you bonuses in ranged combat and AC, into a class that wasn't involved in combat (but see below) and shouldn't be hit ever.
From the beginning, the very rules themselves ensured that a lot of people wouldn't even look at the illusionist. With the possible exception of those weird gnome lovers (no judgement, not here to kink shame) who could multi-class as Illusionist/Thieves or Fighter/Illusionists to take advantage of the abilities.
Second Problem- The Magic Items
AD&D was different than 5e- characters would gain in power by leveling, but a lot of the "specialness" of a character came from magic items. And MUs had a LOT OF MAGIC ITEMS they could use, and there were a lot of magic items that only MUs could use! In fact, a lot of the time, a party would come across a magic item that the MU would get dibs on because only the MU could use it.
The illusionist had, quite literally, the most insane magic item restrictions of any class in 1e (well, until the Barbarian came around in UA and said, "Hold my beer, I need to destroy all the magic items that we got").
You might ask, "How insane?" And I would say- not only was the illusionist not able to use the MU items, the insane restrictions also meant that the illusionist would occasionally be unable to use items that a FIGHTER could use, like a wand of magic missiles!
In addition, because of the way the restrictions are written (some day, I will go into the weird DMG tables about this), no matter what weapons the illusionist uses or chooses from the limited list, the illusionist is only every able to use magic daggers. Or a staff of striking. But no other staves. Not even a +1 quarterstaff.
If the table did not houserule these stupid restrictions, this is just unfair. I often joke that Gygax used every opportunity to take the Thief to the woodshed and nerf it as hard as he could; the reason he didn't do this to the illusionist is because he already did that at the beginning. He looked on his work and he was like, "Yeah, I don't think I can nerf this any harder."
Oh, and the reason for these BS restrictions? According the PHB, it is because illusionist spells are "at least as powerful as normal magic users and possible slightly more potent at very high levels." Which brings us to...
Third Problem- The Spells
Yeah, Gygax lied. Look, let's start with the casual gamer.
Sure. You might not get to that level, but you look at the charts, and you're like, "Um, those spells go to nine. I wanna go to nine." Illusionists? They don't go to nine.
And even before getting into the specifics, a player would then look at the AWESOME spells that illusionists could cast at the highest level. Do you know what a seventh level illusionist spell is?
First Level Magic User Spells
ARGHHHHHHHH! That's right, the Illusionist can use their highest level spell slot (the one with Alter Reality) to learn and cast first level MU spells. I can't even.
Behold, an illusionist at the height of their powers! I can now cast .... MENDING!
I don't want to get into a tit-for-tat on the overall spells. Some decisions just don't make sense (why does the illusionist get continual light as a third level spell, while the MU gets it as a second level spell?), but I think that most people would agree that the Illusionist list is both far less extensive, far less useful overall, and far less powerful than the MU list, and is only
somewhat comparable in the hands of an extremely skilled and ingenious player.
Fourth Problem- Everything else.
Look, at every possible turn the poor Illusionist is screwed. The MU can build a stronghold. The Illusionist? Nope.* Even the most minor things ... MUs get full hit points through the 11th level, but illusionists only get them to 10th level. WHAT? Or if you are into creating and making magic items?
*The DMG does indicate that there are illusionist strongholds. Does Gygax contradict himself? Very well, he does, for Gygax contains multitudes.
Cool cool. Magic Users? GYGAX HAS UR BACK (through complicated and opaque rules). Illusionists? Can only create magic items that "create or sustain illusion." That means that even if an item is within the very limited items the illusionist can use (such as a magic dagger, or a staff of striking, or a potion of healing) the illusionist cannot make one according to the PHB. (Gygax, in a rare un-nerfing, has "secret rules" in the DMG that allow the illusionist, starting at 14th level, to create magic items like a +1 dagger... but no one reads the DMG, and it's just weird that the PHB says that).
Okay. What about the AMAZING XP advantage? At least there is that, right? Well... remember first that with those requirements, a similar MU will have a 10% bonus. That's not nothing. So let's take a look at the following XP amounts:
XP Illusionist (MU) | Illusionist Level | MU Level |
25k (27.5k) | 5 | 5 |
50k (55k) | 6 | 6 |
75k (82.5k) | 7 | 7 |
100k (110k) | 8 | 8 |
250k (275k) | 10 | 10 |
500k (550k) | 11 | 11 |
750k (825k) | 12 | 12 |
...huh. Okay then!
And because the illusionist was such an after thought (I mean, Gygax didn't even bother to come back and nerf it harder) you just didn't see anything for the class. And when you did, it just reinforced your suckage. If you found a book of infinite spells, well, there was a 5% chance for an illusionist spell ... and you should be grateful you were even mentioned.
I could keep going on, but you get the idea. But here's the thing- even if everything else was cool, and the DM was open to illusions, and the player was skilled and utilized the class well, the class was structurally screwed from the beginning. You really had to love the illusionist concept (and/or have an irrational love of an illustration) to play this class.
One final note-
There is one small thing that illusionists could do that people were not always aware of. Given that they are required to have a high dexterity, and given that they will almost certainly be using daggers ... the illusionist will likely be a decent (if VERY fragile) combat support character. They can throw daggers with the dex bonus, and if necessary, the high dex lets them TWF with daggers with almost no penalty. I'm not saying that's a great use of a high dex score, but it's at least something.
Conclusion- I love the 1e illusionist. However, I would also recommend, at a minimum, that tables that go back and use it at least make houserules regarding the magic item restrictions.