NICELY done!!!
I played the original Space Game and enjoyed the heck out of it on slow days at work.
This is a nice enhancement to it!
The new mission types added a nice bit of variety and the difficulty settings covered a pretty broad range from casual playing to hardcore "How the HECK do I do this?"
Contrary to what some people might say about being too hard or impossible from wave after wave being thrown at you, I played through the entire thing on Crazy and definitely had my work out out for me on some levels...but it's doable and often requires just a bit of out-of-the-box thinking (I realize that still seems limiting given how few options there are to play with in this game, but the simplicity is the charm...and there are still non-standard ideas to try).
Music and sound are fitting for the mood, graphics are pleasant..
Fun for a few minutes, or a few days.
100 A++.