[mad=dog]

This being my first post and all (how come people always write that)...

I definitely recommend BG1/TotSC. I have several characters through that combo and are currently trying them out in BG2.
Note that while it is the same Infinity Engine there are some noteworthy differences.
1) Time is not stopped in inventory mode. It took me some time to get used to BG2 as I issued orders and managed inventory while they were being carried out in BG1.
2) If you solo, you don't loose the game if your protagonist is charmed. Moreover charms take forever to run out in BG1.
3) You don't get any XP for scribing scrolls and using thief abilities. (How come there's no XP for pickpocketing in BG2 BTW?).
4) Quicksaving is discouraged by monster generation. New monsters will be generated on top of the ones already present every time you load.
There are other differences as well of course, but these could give you some initial problems.

With TotSC you get two independent quests on top of the main one to complete and you can start one and let another one rest if you like. I liked Durlags Tower a lot although it will give you some nuts equipment compared to the rest of the game.

You also "explore" in BG1 making it more adventurous. You go to the border of a map section and see what lies over the top of the hill so to speak. I find BG1 less linear and less static for that reason alone. I don't really feel like and adventurer in BG2. More like hired help.

Besides all that Imoen is actually likeable and valuable in BG1. Don't know why they ruined her. I really don't. (This is a matter of opinion I guess).