humble minion
Legend
I'll give you a more conclusive answer once we've reached higher level!Does the difference noticeably impact play in those games?
The big difference is that you find yourself playing Healing Word jack-in-the-box a bit less at 2nd/3rd level. You're a bit safer from getting knocked straight to 0hp by one good critical hit .
The by-the-book game is actually Iron Kingdoms, which is a pretty lethal setting (as far as D&D goes) with very little healing magic (we have no cleric in the party) and ranged weapons that do 2d6 or 2d8 damage available from very low levels. My PC is second level in that game, rolled a 2 for her 1d8 for hp at level-up, and has not yet in the entire campaign landed a hit that would NOT have one-shot her from max hp straight down to 0. It's bred a noticeably more cautious game style.
The max-hp-to-level-5 game is a Storm Kings Thunder game, which is now very close to the end. I think the DM in this one wanted to throw giants at us relatively early in the game, rather than having us twiddling our thumbs and fighting filler encounters for the early levels of what is supposed to be a giant-centric campaign, but giants can really deal out the damage if they get into melee, and the extra hp buffer made it less likely that a few bad rolls would TPK.
The max-hp-to-3rd level game is one that I'm GMing. I went with that because we were going to have some inexperienced players and i thought it'd be a good little extra safety net and add to the 'your PCs are the Big Damn Heroes of this world' feel that i was aiming for in a Dragonlance campaign. So far, so good, though admittedly my poor NPCs have had a wildly incompetent run of to-hit rolls so far. I'm a little worried about one PC in the longer term - a barbarian with Dex 18 and Con 16. At 2nd level, AC 17, 30hp and half damage from physical attacks when raging makes him REALLY hard to hurt (I count myself lucky he chose to dual-wield rather than carry a shield I guess..) but he may end up being just so resilient that I'll have to chuck stuff at the group with would be lethal to other PCs in order to even worry him. But I'll see how that goes in the longer run.