Other than the fact that I can't use any fancy graphics mods? Because the games run pretty smoothly on the laptop I have.

Played them on my 4-year old 17" unit. No problems that I can attribute to the laptop form factor. The only slow-down / framerate drop of note occurred when I was engaged in a fight in a flooded room - the water effects caused some choppiness. That could happen on any machine with a lower-end / older GPU, and not just a laptop.

Hmmm, not really if it runs nicely in your laptop. But if I had to find two downsides, that would be:

● Small screen; it's much more immersive in a bigger screen I guess.
● Sound; it's much more immersive with a set of good speakers rather than the laptop's. But you can use headphones and the problem just solved!

Only one - the laptop heating up... and maybe spilling your vodka on it when a bloodsucker jumps out! ;D

I would say the downsides would be up to personal preference, so subjective. Except for possibly one and that being sound. Hearing things around you in the scary parts of the game is quite important for atmosphere so you'll probably want to use some surround headphones if playing on a laptop.