Looked at the Metacritic scores of the first two games.
Valkyria Chronicles 1 has an 86 on PS3.
Valkyria Chronicles 2 has an 83 on PSP.
Personally I loved the first game, while I found the second game to be disappointing. The second game kept putting lots of missions on the same few maps which I didn't like. I want a new map for every mission. The first game is near flawless in my opinion. It is one of my favorite games of all time.
I haven't tried the demo yet. I hope that 4 is just as good as the first one.