IMHO Turrican 1 has the best level design. There a lot of secret places to be found. You will be heavily awarded for exploring; very nice! I first played on the C64 and, yes, I have a soft spot for it. It is a bit rough on the edges compared to T2/T3 though.
Turrican 2 is a technically more advanced T1 but I find it has a little less "soul" than T1. Nevertheless a classic!
Turrican 3 has a bit different gameplay because of the exchange of the rotating gun for the grappling hook. Also you can't jump as high as in the previous games. Also the exploring part is even less than T2. For me the weakest of the series on the Amiga. Still a great game though.
And every Turrican game has great music!
