Welcome to WITP:AE!
I too first looked into WITP so long ago. I remember those days. There were lots of flame wars and opinionated "experts" on what was wrong with the game. For one thing, there's none of that now. At least I don't ever see any. There also aren't any bellyachers (LOL well, maybe one or two) so that's a big relief. It was a real turnoff back in the old WITP days for me.
And that game was much buggier that this. I think it was wise of them back then to issue a broad revamp of so much of it with AE.
Basically, you have to decide if you want more of a game or a historical simulation. Lots of arguments have erupted between these two camps, and it's your decision. Mostly now, people (like me) seem to have decided they want a game over a historical sim. Intelligent people contribute lots of interesting historical facts into the game community in a way that makes all that very interesting, without the heat. This has created an excellent mod community that have the skills and interests to put together mods that they believe presents differences they consider important. The broader community gives them a try, knowing how the mods differ up front. You can find one and play what you like, and even make one of your own. Open it up to the community, it may become a hit. Several have.
People find their enjoyment in recreating/rewriting history, and that's fine. Plenty of people do here. But for me, I googled for quite awhile to find the most complex, challenging and historically-based computer wargame I could find. Basically, I wanted a game I'd never be able to exhaust myself on and get bored with. I'm not into space rangers or fantasy monsters, mind you. Boy is this ever it!
So for me, it's basically Red Team versus Rainbow Team, using almost every ship and plane and commander across half the planet, in day turns, for years. And the algorithms that control the game are more than good enough that it rewards good play, but inaccessible and unpredictable enough so no one games the system.
The map choices are remarkable. I'm not that into primary colors myself, I prefer a more satellite-imagery approach although it would drive other people nuts. It's there, and some of the maps offered are works of art. Concerning the maps, I think the community generally agrees, for instance, that there shouldn't be a river between Diamond Harbor and Calcutta. And I remember measuring the air distance between Port Blair (and southern Sumatra) to the sountern tip of India, and I think the map has them too close together. But it's a very, very minor nit to pick.
Bug-free? 99% yes. There is what is referred to as the "Synch Bug", where two PBEM players have slightly different versions of upgrades and/or mods. It doesn't happen often and is prevented by closely comparing versions prior to play.
Is the vanilla version fine? Yes, for me. Scen I is all I'll concentrate on for the forseeable future. I'll consider it a major accomplishment in my gaming life if I can offer a reasonably good game in just Scen I! People say though, that for better play against the AI, the "Ironman" scenarios offer a more challenging game in solo play.
But let me say in no uncertain terms I think one of the best parts of WITP:AE is the community. There are some very fine people here. The others have been weeded out by a game this complex and challenging that usually takes years to commit to play. And I've been impressed by the numbers of more recent players that have become amazing at the game in what seems (to me) to be a very short period of time. It's important though, to RTFM and the forums/AARs as much on your own as you can (ie steep learning curve ahead!). The Matrix search function leaves something to be desired. Use Google, ref WITP:AE. The upgrades have improved things alot, but some of the changes aren't reflected in the paper/pdf game manual. People will fill you in on those changes as you go along. Some of them are stickies in the forums.
Then there's senior forumite Alfred. He's part archivist, game historian, and game concept and algorithm guru. I humbly suggest you pay especially close attention to his postings on subjects. There isn't anyone that can clear up game questions like he can AFAIK. I have considered for years now starting a fund for him to take the time to compile a new game manual. The game is so vast, it would take a lot of time, and I'd support an honorarium for him to be compensated for his time and effort.
So, that's about it elxaime. This game's been a blast for me. I hope it is for you as well!