Justicar of Doom!
The scoring is misleading because there is one final mission that ends the game but you don't have to do it right when it appears. You can play an infinite number of random side missions.
Playing more missions until all your squads hit level 20 is not a bad idea. Playing more to get some awesome blue item, ok. But eventually just grinding up to the max points of 100,000 seems like not so much fun.
When you win the last mission it creates 2 save files.
One after the win, so you can see the ending stats, but no more play.
One save is just before doing that last mission, so you can continue doing more side missions. A very nice idea, since there is no way to make additional saves, except for copying/renaming files.