There are quite a few cosmetic differences between the two:
- Different headlights (much better!)
- front bar with round indicator and spotlight (series 2)
- Dash fascia has rough finish rather than smooth for series 1
- Rear 'SKYLINE' lettering on bootlid is in same colour as car for series 2, as opposed to in clear plastic for series 1
- Higher boot spoiler on series 2, although did come out on '95 model series 1.
- Interior cloth trim different on series 2
Also you'll get twin airbags as standard in series 2, '93-'94 driver's airbag option, '95 driver's air bag standard. Not sure about ABS, I think it's an option on series 1, standard on series 2 (Don't quote me on that one!!)
Also some electrical components on engine are different, eg. coil packs
There might be more but that's what I have discovered anyway....
Hope it is of some help,
Cheers