I remember when Acid was released people dogged all over it because it wasn't a traditional Metal Gear game but both titles are fun in there own way. The second is more bright, colorful, and follows a cell shaded style but the gameplay is still there just expanded upon.
Also I don't know what your particular gripe is with Peace Walker but I commonly hear that people can't stand not being able to go prone in that game. If that is one of your issues Metal Gear Portable Ops has a bigger emphasis on stealth elements rather then the action emphasis in Peace Walker so you might prefer that title.
Earlier in the thread you said you were interested in picking up FF4: The Complete Collection and if your a fan of the original game you should go for it.