Ok, an admission - I didn't like the original Commandos. Fun, yes, but ultimately unsatisfying.
Commandos 2, however, is a different story - one of the best PC strategy games you could ever play.
It took everything that was good about the original - the mixture of tense stealth and all-out action, the evocative landscapes, and inspired riffing on classic WWII themes - and polished it to near perfection.
This game is a labour of love, and proves that in gaming, it's the little details that count. Every tiny aspect of so beautifully realised: the graphics of every part of the German / Pacific landscape; the animation of the characters; the sounds; everything: and the result is a game that draws you in to its Boys' Own world of meaty heroes, stiff upper lips and scheming Nazis. No other game delivers so much action, tension, thoughtfulness, humour or replayability.
It has been criticised for being fiddly and difficult. True, it takes more concentration that more immediate action/strategies like Diablo, but in fact it's so open to player choice that you are free to go Oppenheimer with a machine gun if you tire of sneaking.
Commandos 3, sadly, was nowhere near so well received, but worth having if it means you can get C" safely on your hard drive. Treat yourself to a true gem!