I used to play SuperPower 1 and 2 back in the day, and had fun with both. Having lost both games over time for one reason or another, I decided to purchase Superpower 2 for Steam for nostalgic purposes. What I encountered was a little underwhelming.
As other reviewers have pointed out, realism pretty much flies out the door with this one. One time I played as Croatia and, after an hour of play, had China randomly invade and annex me. In another game I watched online, Italy invaded and annexed China, then started eating up African countries, with no one in the world seemingly caring. I know there are realism mods out there, but as is, the game leaves much to be desired in this regard.
Related to this is how the game's mechanics react to your decisions. Example: I started with a multi-party democracy nation with basic political freedoms, and then - practically overnight - outlawed every religion and language except one, removed freedom of contraception, freedom of speech, freedom of assembly, then transformed the government into a military dictatorship. You know what the drop in popular support was? MAYBE like 5%. I'm not kidding. It went back to normal after a while. Government stability didn't take a hit either. I had done this to see just how insane my nation would go, but discovered that it didn't do anything even negative in the short-term. For a supposed geopolitical simulator, that's a bit lacking.
One of the most aggravating aspects of this game is the economic model. At first glance, it can seem like a wonderful simulation of the world trade, but after trying to figure the thing out...I just can't make a surplus. Well, to be fair, I did once, but I don't even remember how I did it. I've tried various methods, and I've read tutorials online on how to set up your economy, but nothing seems to work. I've dealt with the economic models in other games from a variety of developers, and even if they were at first difficult, I managed to figure them out after a while. SP2, however, has a model that will aggravate the casual gamer and give them headaches, trying to figure out how to keep those numbers from getting red again.
One of the few things I appreciate about this game is the way wars and armies are done. Unlike SP1, which were a bit more clustered and limited to various cities, you can move armies around the map like you could in real life, and let them engage across a wider front. It's fun to see the symbols flying around on the spec-ops-style map, and watch the battles between two sides unfold.
Is SP2 worth purchasing? I honestly don't think it's worth even $10. It can be that one game you take out every year and play for a while, before you remember why you uninstalled it in the first place, but it probably won't be something you play on a regular basis.