I just worship the illusion school. Silent Image, Phantasmal Force (AD&D), are my favorite spells. Illusions are, (the way I see it anyway) the epitome of magic. When we say that a wizard can distort reality, illusions are the first thing that spring to my mind.
Illusions = Creativity let loose.
Yet, no matter how cool those illusions are, or how powerful they might look... the end result is that they ALL get tramped by a single cantrip ... the accursed DETECT MAGIC (and its big brother = Arcane Sight)
I 've been searching about this in the web the past few days (on old threads of the site ...and of others), and thankfully I found out that there are a lot of gamers out there who share the same opinion, and they were mostly DMs, whining about how they can't make a proper trap or decent illusion based encounter without having this cantrip ruining it for them. Worst case scenario? A character who gets a permanent detect magic/arcane sight on him. This is bye bye to the DMs plans.
Examples of this tiny divination thwarting every possible encounter based on illusions are endless (traps, disguises, secret doors etc etc etc...). Admittedly, this sucks.
The simplest explanation one can give, as to why this happens is the following:
The power of an illusion is that it deceives you for being real. Once you know its an illusion, it loses all it's power. And Detect Magic, this 0 level miracle, grants you this ability without even a miss chance, not to mention arcane sight....
All other schools of magic do not lose their power once detected. Even abjurations, or other traps with necromancy, enchantment and stuff do not get all that weakened, because even if you detect them, you still have to find a way to overcome the actual effect. Illusions on the other hand, are COMPLETELY useless once detected.
To be more precise, so as to fathom the full extent of this problem, lets see which (and consequently the big number of) spells that get thwarted by Detect Magic and its derivatives.
1st level:
Disguise Self (100% busted)
Silent Image (100% busted)
Ventriloquism (it is arguable... but still possible in some situations)
2nd level:
Minor Image (100% busted)
Phantom Trap (100% busted)
Invisibility (Very difficult to thwart during combat because of the 3 round process and the rotation of the cone which might cost more time. Outside of combat though, an infiltrator gets 100% busted, no matter the 50% miss chance. He's busted. Arcane sight tears Invisibility apart. You instantly get to pinpoint and allow for attacks with a 50% miss chance as well as area effects. Also 100% busted in case of infiltration)
Mirror image (Almsot Impossible to thwart in combat. Arcane Sight nails it if the real PC "carries" other auras on him... which is the case 99,999% of the time...)
3rd level:
Invisibility Sphere (As Invisibility)
Illusory Script (100% busted)
Major Image (100% busted)
4th level:
Hallucinatory Terrain (100% busted)
Illusory Wall (100% busted)
Invisibility, Greater (Detect magic will prove to be almost worthless cause this one is used in combat only, Arcane sight though, breaks it, as usual)
5th level:
Mirage Arcana (100% busted)
Persistent Image (100% busted)
Seeming (100% busted)
6th level:
Mislead (100% busted)
Permanent Image (100% busted)
Programmed Image (100% busted)
Veil (100% busted)
7th level:
Invisibility, Mass (As Invisibility)
Project Image (Only Arcane sight can truly help here... it's VERY helpful to know you are not fighting the real thing)
No need to mention that the minimum 3 round process of detect magic is NO PROBLEM AT ALL in situations outside of combat (Most of the above spells will be detected in situations outside of combat). When searching rooms, interacting with disguised NPCs and stuff a character usually has enough to plenty of time to use Detect Magic.
Now a few solutions I've found to this problem, in order to balance out Illusions and Detect Magic (+ Arcane Sight accordingly), are the following possible house rules:
(Those are not to be combined. Each one is a separate solution)
....Personally I prefer #3. Surely the most advantageous to Illusions.
Tell me what you think.