HereForTheBeer: I have not played the first one, so...

It sounds like 1 is more mission-oriented than 2, whereas 2 lets you free-form and explore quite a bit between the story missions.

2 gives you a bit of a trading feel, but I wouldn't brand it as a true "outer space trading game" since you're not doing it for economic reasons except in maybe one or two cases related to mission requirements. You get new ships as part of the storyline, and your trading is limited to obtaining equipment for your ship. The trading element goes something like, "this faction has ship component ABC and is looking for commodity type XYZ." This is both good and bad. If you can't find the commodity necessary to satisfy the trade, then you may have to waite a while to get that component. However, this also encourages exploration as you try to find that commodity among the stars... and pirate it. Heh.

In one area, space sims tend to excel, and that's graphical awesomeness. 2 does not disappoint, looking as good as anything out there.

I-War 2 has some clever missions that have you doing things other than "kill them 'til they die from it," and there aren't a whole lot of FEDEX-style missions to slog through. There are a few points in the game, namely early in Chapter Two, where you're left sort of wondering what you're supposed to do next, but there is also an add-on to the game that gives you a story walk-through without too much in the way of spoilers. It's more of a "here's what you need to do," instead of "here's how you do it."

Good luck choosing, but I'll recommend starting at the first and eventually buying the second.