Yes, they're some of the best (and most complex) RPGs you will *ever* play. Games like Mass Effect and Kotor evolved/drew very very heavily from the Baldur's Gate games, often sacrificing depth and complexity for easier combat mechanics to make the game more accessible (which is fine, those games were still great in their own right). But if you want to see where it all began, and appreciate some really intense gameplay, check out BG.
This is a guide [http://www.gog.com/news/enhance_the_gameplay_in_your_edition_of_baldurs_gate_from_gogcom] to run BG1 and BG2 as one long, continuous game all using BG2's mechanics. It also includes patches and commonly-used player mods, for things like obtaining multiple strongholds and getting access to additional merchants. It takes an hour or so to patch it fully, but it is definitely worth it. You will get hundreds of hours out of this game, easily.
Re: needing to read D&D manuals... you don't, really. There are a few confusing mechanics, the leading two are probably THAC0 and the entire casting system. TLDR versions: the lower your armor class, the better (don't freak out when full plate "drops" your armor to 1 when your chain mail gave you 4, that's how it's supposed to work). For spells, you have to prepare them in your spellbook, and then rest somewhere for them to be castable. To "recharge" your spells, you have to rest again. Wizards learn spells by reading scrolls, Sorcerers pick spells as they level, and Druids/Clerics have preset spell pools. Every other mechanic should be obvious as you encounter it. Mostly.
Edit: Fair warning, the most jarring thing people notice when I get them into this game is the lack of quest markers. Your hand is not held in Baldur's Gate. You have a journal which doubles as a quest log; get used to reading it. Snippets from NPC chatter, rumors you hear at a bar, or quest updates will all be found in the journal, and if you don't pay attention to it you can wander around not knowing what to do for a very long time.
