I know it's considered a classic, and as a fan of turn based strategy, I've always wanted to give it a go, but three things I want to ask:

1. Is the game on Direct2Drive optimized to work on modern setups or do I need some workaround like DOS box for this? How are the older games in general on D2D?

2. Have the games aged to the point that nostalgia is what's keeping them afloat? I had that happen to me with Fallout, as it was just ridiculously dated by the time I finally got to play it, and I don't want it to happen here also.

3. It includes all 5 games in the series. Which are good and which aren't worth bothering to play?

I don't know anything about D2D but I can tell you that the first and maybe the second are the only ones worth getting and the game is rather dated and has some qwerks/bugs that are quite annoying like not being able to load during a mission forcing you to quit before loading, that gets annoying if you are getting slaughtered by mutons. also their is a learning curve that may put you off if you are easily discouraged. But once you get into it can be a very rewording experience.

why not get it on steam?

Why? What's the difference? The reason I'm considering it is because D2D is running a sale and the bundle is $5. Does it cost that much on Steam?

I have it on Steam (came with Civ4, Civ 3, BioShock, etc, for 45 bucks) and it works just fine. Original XCOM is not held up by nostalgia at all. If you find me a current TBS as deep as this one do let me know.

Hey buddy! Thanks. That's very helpful. So I'm getting five games. Which of these are good and which are bad? I know at least one is some sort of spinoff.

1 and 2, UFO defense and Terror from the Deep. You can skip the rest.

Wow. That bad?

They weren't that bad. They just weren't as good.

Also I'm not kidding for the 2K pack thing. It also came with all the Freedom Force games, Sid Mier's Pirates!, a bunch more and I even think Deus Ex, on top of Civ 4 and civ 3 complete.

3 is ok too if you aren't expecting something as good as 1&2. BTW i suggest playing them on netbook if you have it as resolution in 1&2 are rather bad.