Shucks! That's bad! I guess SC: Chaos Theory was way better. I can still think of re-doing an entire mission but what angers me more are game crashes to desktop...that drives me mad! Does this happen a lot in this game?
There are certain places where it always happens, but otherwise it's pretty random. You need to save regularly as it may crash at any time. I had maybe 15 or 20 of these random crashes throughout the game.
I did manage to complete the game, but there were two points in mission 8 where the game always crashed as you entered a save checkpoint, and you were forced to trigger the checkpoint to proceed with the level. I had to edit the game's ini files to bind a key to a cheat (thank goodness for the Unreal engine's ghost command), so I could fly around the checkpoints and prevent it from saving.

I seem to have lucked out though, as I've read about a lot of problems on mission 5 as well, and also many people reporting that saving a game
anywhere in one map in mission 8 causes an immediate crash.
Apart from the crashes, there are also several places where some ingame scripting doesn't work and makes a mission impossible. At one point, a guy is supposed to turn around and you have to crack a safe behind his back, but he had gotten stuck on some level geometry and kept looking back due to that. I think I ended up showing myself there and just took the hit on the trust level. There are also numerous odd glitches with the menus and UI. For instance, you'll find that Sam refuses to perform certain actions, like safecracking or entering vents, unless he is running at top speed (this is at least easy to work around). To add to everything else the graphics engine is very poorly optimized; it's essentially the same as CT's engine but runs at maybe 1/4 the framerate.
I have seriously never seen a game that is so frustrating due to bugs. This could have been quite a good game but it was essentially released in an alpha state, and there won't be any further patches for it. It doesn't hold a candle to CT.