The GT 635m is marginally better than an Intel IGP, but a laptop really should have a GT 645m, I believe ~~ gotta do some checking. Also, Geforce cards will shirk their work if you don't make certain they are switching on when the 3D starts. The Intel IGP is really poor, and fails pretty miserably when the Optimus card won't switch in.
The Geforce support forums will help you understand the setting in the Geforce Control Center that you must make sure are set correctly (sadly enough, a large percentage, perhaps as many as a quarter part, of the Geforce Optimus switching GPUs won't make the 3D switch in gaming in all games at this point in time).
https://forums.geforce.com/
P. S. I looked up the GT 635m, and it looks MUCH worse in comparison than I expected:
http://gpuboss.com/gpus/GeForce-GT-8800-vs-GeForce-GT-635M
I think I will see about the 645m, even though you cannot upgrade to it.