Now, the following is simply my opinion on the matter, so please don't berate me for this: 2nd Edition AD&D is too restrictive, particularly so with druids. Yes, BG is more flexible than PnP, but the simple fact is that for all druids get, you may as well take ranger/cleric. Druids just aren't that pretty, and while there are plenty of PnP reasons why they have such a steep experience curve, it just deters people away from the class in BG2. While clerics, mages and even ranger/clerics are shooting off into level 20, you'll have just squeezed past level 14, which I think is really disheartening.
The shapeshift forms are particularly bad, including the forms from the shapeshifter kit. You sacrifice spellcasting to become a walking sponge, in the grand scheme of things. I admit that the BG2tweaks change to the shapeshifter kit was kind of overpowered, but here's the thing: it was playable! You still weren't as powerful as a well-kitted out cleric with a decent weapon and magical full-plate. That and you'd still take damage, frequently.
I believe it was also bg2tweaks that introduced changes to the experience tables of druids and made them mirror that of a cleric's. I'm not saying Overhaul should use these changes, but perhaps just create their own experience tables. Druids do have their strengths, but much less so than many other classes. They're not the worst class in the game, of course not. Bards could potentially win that competition. However, I don't like the idea of having so many underwhelming abilities that sound great, but aren't, and having a very long period of waiting while the rest of my party exceeds me by 6 levels.
Since combat is the core of BG, and roleplay really only bubbles down to the player's choices and stat distributions, I think one or two PnP restrictions should be lifted from the original game in order to provide a more pleasurable experience.
Show nature some love!