So here's what I'm thinking:2. 4e HP solves the annoying problem of "we have to have a cleric!"
This was an extreme nuisance in D&D. First of all, I don't think that any party should have to have a specific class. That is stupid, though having a wider selection of tools to approach a problem isn't a bad thing. 4e allows one to have a party of all magic-less characters, which makes me happy.
Secondly, it's kind of...moronic, shall we say, that divine magic is the only way that characters could be healed magically. Unless you had a bard. Because bards have special arcane magic that allows them to use spells normally reserved for divine magic.
EDIT: As one poster notes, clerics technically aren't REQUIRED for D&D play. Instead of a cleric, you have the following options in 3e (at low levels):
1. A bard who heals 2 HP per day with his awesome cantrips.
2. A druid who wastes his spells memorizing CLW.
3. External research (DM fiat territory).
4. Extra Spell (DM fiat again, and a waste of a feat).
5. A week of recuperation after every fight.
6. An NPC healer.
7. Wands of CLW.
My personal solution would be as follows:
1. Expand the Heal skill.
2. Give healing options to other classes (bards having a healing song, rangers able to make poultices and stuff, etc.).
3. Make magical healing accessible to arcane casters.
However, 4e solves the problem in an alternative manner, one that I don't particularly like, but a simpler manner nonetheless.
3. 4e HP solves the low-level problem of damage input not matching damage output.
Look at a first-level orc in 3e. It has 5 HP. It also has the ability to do up to 12 points of damage on a normal hit, and it could do up to 24 points of damage on a crit (which it would threaten 15% of the time). That little CR 1/2 orc, the one that could barely take a single dagger cut? He can cleave the party fighter in two with ease, and the party wizard is going to make any Jodie Foster character look healthy once he's done fighting the orc.
4a. 4e HP solves the problem of one fighter getting 10 HP a level and another fighter getting 2 HP a level.
I'm pretty sure it's happened to everyone. The party wizard gets a 4 when rolling for HP while the party fighter gets a 1. Sucks, doesn't it? And while this should even out over the long run, you're still screwed at low levels because monsters will beat the fighter's face in while laughing at him for having 18 HP while the party wizard has 12.
4b. 4e HP solves the problem where the DM has to guess-and-check to see if an encounter is appropriate for the HP of his players.
4e HP narrows the gap between what HP is, what it ought to be, and what it could be. In 3e, your level 10 fighter is going to have something like 10 + 9d10 + (10 x your Con modifier) HP. Giving the level 10 fighter a Con modifier of +4, that means that he's going to have between 59 and 140 HP. Pretty big difference there. Again, while that should average out, it doesn't mean that it's going to. Give the fighter another five levels and he might roll nines or tens for his HP, bringing him back up to par, but that doesn't mean that he's not going to roll poorly, widening the gap between what he ought to have and what he does have.
5a. 4e HP does not solve the problem of "infinite magical healing."
EDIT: Personally, I do not think that "infinite magical healing" is a problem. However, I have seen many people gripe about it, so I'm including it in this post.
I hate CLW wands. I hate them so very, very much. 50d8+50 healing for 750 gp is annoying. Very, very annoying. Not only does it trivialize HP recovery overall [EDIT: not that high-level characters have much to worry about in this regard, mind you], it creates scenarios where the party stands there for five minutes while Billy the Cleric pokes everyone with his hand.
However, 4e HP doesn't solve this problem because everyone gets full HP at the end of the day anyhow. Give everyone a good night's sleep and they wake up at full power the next day. There's no real difference between the ends, only the means.
5b. 4e HP does solve the problem of, "Crap, we're wounded, so we'd better rest for three days in the middle of this swamp to get our HP back.
EDIT: Since people seem to have difficulty understanding what I'm saying, allow me to clarify: there are problems in the 3e system of HP recovery, and there are problems in the 4e system of HP recovery. As an individual who doesn't treat editions like most people treat political parties--where 3e craps sunshine and rainbows and 4e puts orphans into blenders--I am perfectly capable of critiquing the systems in an unbiased fashion. While I am against 4e overall, that does not automatically mean that I think that 3e is perfect. In fact, I think that 3e is pretty much broken outside of a huge rules overhaul.
Since you get all your HP back in one rest period, you don't have to rest for a day, have the cleric spend all his spell slots casting CLW, rest for another day, and repeat until everyone has full HP. (This is a good thing.)
6. 4e HP makes it impossible for adventurers to take any real wounds without dying.
Because of the method of HP recovery, there is no possible way that any adventurer can actually become severely injured in 4e. (Seriously, we have hundreds of pages on these forums arguing about it. The pro-4e response is pretty unanimous: no real wounds.) I think that's lame. You might disagree, but I think it's stupid that the most damaging wounds you have are going to be nicks and scratches.
EDIT: "Severely injured" in terms of flavor, not mechanics.
It has been repeatedly suggested by the pro-4e crowd that you can't determine the extent of an injury until after you make your death rolls or whatever they're called. So basically, you get knocked out, and you roll until you die or recover. If you recover, you actually only took a graze to the head that knocked you over; if you die, the troll's hammer shattered your skull, sending grey matter everywhere. (That would be a slight exaggeration, for those of you who are going to take that example literally.)
3e doesn't model this very well, either, but there's some realism in that a fighter with 200 HP getting dropped to -5 and recovering on his own is going to take many days of recuperation without magical healing.
4e HP is fail. Characters have Hollywood Healing. Healing surges make me roll my eyes. However, my question is: is the lameness of Hollywood Healing worth the "less downtime" aspect of healing (at low levels) in 3e? Or would it be better to go with the "more ways of healing up" for the sake of verisimilitude?