With the ready availability of curing magic and potion, people don't heal naturally really very often at all -- you only rest if the spellcasters need it, not because you're too wounded to continue. A wand of
Cure Light Wounds, with 50 CLW's, pretty much alleviates the hit-point need to rest, period.
As for the rest of this:
Yeah immunity is always good, but other than energy drain and air I'm thinking so what. Really how often is there disease in the game at all, I mean sure occasionally some one might cast contagian but other than that??. And poison while immunity to it is potent its rare enough that I don't care much. Fatigue, exaustion, food, drink I could care less. I don't have many PCs working at the coal mines so fatige and exaustion only come up when I throw a maroon at them who is stupid enough to cast those lame spells in 3.5 that cause it. And no eating, on no he saves 5gp a week. Paralysis is potent but elves are immune to the most frequent sort I'm used to seeing which is the ghouls touch and it hasn't broken anything.
No need to breathe on its surface isn't a big deal and probaly isn't but there may be some creative uses with it and underwater dealings that may throw things off. But hey a 3rd level spell lets the whole party breathe underwater so its probaly not a big deal.
Energy drain though is one of the big pains in the butt at all levels past like 5 so immunity to that would be strong, but I'm not so sure its game breaking.
This very strongly depends on the DM and their take on the campaign, and their use of certain enemies. For instance:
1 - in a plot based on a siege, disease could be very obnoxious -- all it takes is one person who doesn't get the
Cure Disease spell, and the whole city is crawling with it again. Consider also plots based around dumping grounds, traveling through sewers, etc. While all the rest of the PC's are bedridden with diseases, the warforged calls them all pansies and saves the world on his own; he's the only one who's not hurting from this. Admittedly, your average dwarf doesn't easily succumb to disease either, but having a bonus to a save or an ability score is a world apart from having outright immunity (in addition, disease has gotten a poor rap in general IMHO, so I've ratcheted up the disease problems IMC -- like the Nyambe idea of having diseases with SR)
2 - Poison is pretty huge...there's a lot of monsters with it (especially natural monsters), and a lot of enemies like to use it (especially roguish enemies), and it remains dangerous into the high levels (no one likes seeing their CON drop...). It's a great equalizer, and it remains a potent DM tool to threaten the party....but not so much anymore...a Warforged can't be threatened with poison at all. Again, a dwarf might not have a lot of troubles with poison either, but I'd rather give the Warforged a +x bonus than give them outright immunity anyday.
3 - Fatigue and exhaustion come up frequently IMC, because enemies know that one night of sleep = all your spells back, so if they can stop the PC's from resting, they can stop the PC's from casting spells, and thus can weaken one of their greatest weapons. If you don't get a full night of sleep, you gain fatigue, you gain exhaustion. In addition, the fact that these two conditions *stack* makes them savage for anything without a good Fort save, and dangerous even for them. Sure, Warforged robo-men should not fatigue easily, but they should still fatigue. Think of all the adventures in which the heroes are run ragged by the enemy, breathing down their necks at every turn....with a warforged, that suspense is gone...they can keep it up alllll day.
4 - Food and Drink come into play with the nickel-and-diming of the PC rescources which is very popular, especially at low levels. Though IMHO, this is not a very big deal, either, it's still a power, and it gets more onerous because they included a lot more....for Warforged, it just requires a slight adjustment interminology...food & drink become the energy that they need to power on...it hurts my verisimilitude more than anything....*everything* needs a power source, ne?
5 - Paralysis hurts a DM who likes to handicap their low-Fort-save-PC's. Since I don't know of any mundane effects that cause paralysis, this is pretty much a magic-only region, and I see no reason that they should be immune to paralysis...and it removes another potent 'even-high-levels-are-threatened-by-it' weapon from the enemy's arsenal.
6 - a 3rd level spell is a big deal if every critter does it. Unless you don't think it's a big problem giving gnomes the ability to cast
fireball whenever they want?
No breath means no suffocation, means no slow death or inhaled poisons or underwater challenges or choking or anything...
7 - Energy drain basically means that any DM who wants to use Undead as the main adversaries is SOL against the Warforged. They can't threaten his most powerful asset like they can threaten everyone else's.
So you see that these are subjective; not everyone has the same campaigns, and it'd be better, I think, if the Warforged were *good* against those threats, but I see no reason to make them completely immune to them....they could traipse through a field of poisonous underwater undead vipers for 100 years and never be worse for the wear.....that just doesn't make *sense* to me.