Which to start with? 4 or 5?

[Hugh Manatee]

SEV's UI isn't "horrific", it could be better, but it's far from horrifying, and Kwok's balance mod is fun and the hex grids, 3D simultaneous space battles are cool. MoO3's ui otoh... *shudders* it's like that face melting head exploding scene from raiders of the lost ark.... THAT's horrifying, and SEV ain't nowhere near that.

[Black_Knyght]

Definitely go with SEIV, and don't even bother with SEV.

[Captain Kwok]

I suggest you try SE5 as well once you become familiar with the general gameplay of the SE series. SE5 has more features and generally better gameplay IMO, but its UI is less intuitive versus SE4 and its performance in Vista isn't too great.