I wouldn't call AP fantastic but I thought the gameplay was perfectly enjoyable, but really not worth a second playthrough.
I always find it hilarious how many people can't handle the boss fights in DX and AP. Granted, AP made the awful choice of having the weapon skills really limiting your shooting abilities, but, come on, HALF your stats involved weapons, nearly every bit of gear you found or could buy was a better gun. Stealth is fun, but you guys have to be ready for the swerve. You KNOW you're going to have to shoot someone before the credits roll. The game is clearly built off Syphon Filter, not Splinter Cell.
And, of course, in DX, you CAN'T suck with weapons, and even if you take every non-typhoon combat aug, you STILL won't have measurably better survivability against the bosses. Sneaky nerd Jensen fights the bosses the same way as Shoot'n McHeadshot Jensen