I really dislike the limitations removed on a lot of skills like cast delays and summons. The game is way too spammy in full groups like this and the screen way too cluttered. It just looks bad. One of the things I always liked about D2 was that the skill effects weren't over done and this mod pretty much ruins that aspect of the game. It was always amazing to me how D2 managed to fit so many mobs, players, item drops and skill effects into an 800x600 window without cluttering things up too much. When you look at games like D3 and PoE being played at 3840x2160 in a single player game the screen is often more cluttered than D2 at 800x600 under the most extreme of circumstances. Not anymore.
I'm also not a fan of Corruptions. This is the same idea as Vaal orbs from PoE. One of the great things about Diablo 2 is the items you find are satisfying because they're often valuable. Right now players still are valuing item drops as valuable. As time goes on I think what will happen is item drops will lose value and they will need to have a good Corruption on them to be seen as valuable because every good Corrupted item is significantly better than the item you find as is. This fact makes finding an item feel less rewarding or satsifying.
I'm iffy on Maps. They seem to be done okay in PD2. They don't seem to really replace Baal runs until much, much later on in the leveling grind and that's how they should stay. I hate the way PoE maps feel like the entire game. Best place to level. Best place to find items. Maps are a good idea if they're a long grind relegated to the very, very end of the game not like in PoE.
Lastly the best part of Project Diablo 2 has already been available for ages. The widescreen mod, cnc-directdraw w/ shaders, Basemod's shift+click stash, BH loot filters and an even better "infinite" stash w/ PlugY can all be played without all the obnoxious gameplay changes from PD2. If someone would just make a centralized server for these mods without adding all the extra crap from PD2 or PoD that would be a mod I'd be really interested in. Throw in some fixes for longstanding bugs and you basically have a D2 remastered.