Both are good games, and the core rules are fairly simple (3d6 roll low). However, they both offer tons and tons of options. This is kind of like having a $10,000 mechanics tool chest with all the doodads, when all you really need is a ratchet set. While everything you can possibly want is in there somewhere, you have to basically know ALL of the rules in order to find the things you want, and to know how the various skills or powers you are not allowing will affect a game.
While you can maybe get away with a general knowledge of stuff to make your decisions, you still have to read everything. I think many people who make the argument that the "base rules are really simple" just completely miss that fact.
What also has really hurt both games, IMO, is that they are now split up into two separate books. Instead of having everything organized in just one rulebook, you now have to have both books open if your running combats (unless you're one of those people who has actually memorized everything). This is clumsy to handle at the table, and also makes looking up rules during play a major hassle. Especially if you think a rule is in book two, but is actually tucked away in a powers description in book one.
This is one of the areas that D&D has improved. By moving characters and combat into the same book (and lately even treasure), players and the DM can find everything much more quickly, if there's a question during play. Hero and Gurps are moving in the opposite direction, and I believe that's a big mistake.