I love this game. Beside silly haircuts, clothes and gadgets, the story revolves around moon-stones, earthquake-inducing LASERS and such things. It all fits quite neatly in the 1970s jive, when everything was over-the-top. Dialogues are quite funny too: "Police got new teletyping machines that can send a whole printed page thousands of miles away in just TWO minutes!" :D
Gameplay is fun, and that's what matters. Of course there are many switches in each level - it's a puzzle game! But there are many different ways to solve those puzzles (even some that probably weren't planned - like using the robot for teasing the guards). All commands can be given during a pause, so you don't need ninja reflexes to play. Characters have unique abilities, but others can perform most of those feats too (except Rocket's vent crawling and Robo's invisibility) by using tools, which you can buy or find on the map. Meaning, you'll play a level very differently with different crooks.
At first I was quite mad 'coz some levels couldn't be completed perfectly. Then I realized you *weren't supposed to* in the first run. You can replay them for 100%, AFTER unlocking new abilities. (Though I still managed to get all the loot during the first run in all levels but two - without being seen once.)
Challenge mode is much harder, with tougher guards and tight time limits. So re-playability is quite high.
Beside manual saves, the game has a really neat autosave feature, saving every half-a-minute or so, thus allowing you to experiment freely, not requiring a level-restart for every single mistake (like Commandos do for example).
So why just 4/5 mark? It's mostly bug-free, but there *is* one very nasty bug, which corrupts every file, saved while guards are alerted (including autosaves). So you need to save BEFORE you lure guards away (by making noise or whatever), then go without saving and making any mistakes until the alert ceases, which can be quite frustrating. If they fix this I give it 5/5.
