I have an R33 GTS-4 (project thread in this section of the forum) and as BADHABIT says it has the Atessa 4WD system found in the R33 GTR, though the non V-Spec version I believe so the rear LSD is not the Active-LSD.
I don't think the R33 allows "switching" the front drive off, but you can fit a Torque Split Controller/Converter that gives the ability to override (trick) the 4WD to not come on as quickly or vice versa. All of that is covered elsewhere.
Pretty fun car to own. I'm only just completely used to the way the 4WD kicks in now and it is exactly as BADHABIT says, keep your foot down
The biggest gripe with them from my point of view is the mix of suspension used as they have GTR front shocks and GTS-T rears so finding aftermarket suspension kits is a pig.
As for engine differences, they have the same RB25DE found in any of the other non turbo 2.5l Skylines apart from the block has a different sump bolt pattern because of the 4WD sump (so no easy swap to an RB25DET unless you get one from a Stagea).
Brakes are a bit crappy as well, and they are the 4 stud pattern found on the other non turbo skylines. You can fit GTS-T calipers etc pretty easily but you need to get the discs re-drilled for correct stud pattern.
I'm concious I've just listed the majority of the issues I've come across so I'll finish by saying my GTS-4 has been a joy to own so far and really (touch wood) pretty inexpensive to service/maintain compared to perhaps the GTS-T/GTR. The 4WD is an added bonus and you always have the option of dropping in a GTR engine at a later date!