I think that B5 is D20 with some heavy mods... can't remember if all the Skills and Feats and character advancement is in the book (I have not looked at my rules for a while now, sooo many other game books to read)
The big chance is that Hit Points don't go up very fast (I think the best get 2 or 3 points every level AND no CON modifier). Your Ref save gives you a bonus to your Defense also, and Armor I think is a DR.
They used a lot of the same rules for Starship Troopers (that I just picked up), except that one is OGL
NOTE that you can pick up the Pocket B5... it is all B&W, not many pictures BUT it has all the rules and the plot stuff in the back just like the big colored version of the book