Definitely good for one who likes to play games in small chunks
Story:
The story in Unit 13 is practically non-existent. Summarized all together, it's basically about a special task force called Unit 13 (13 comes from the Death Card in the tarot deck or so it says in the manual), and at the start you play as a character who just joined, nicknamed "Animal" and he apparently has a really cool beard. Besides that, it's all about killing terrorists with a brief description as to what's happening which is so uninteresting I doubt most players will even bother reading it. The characters you play as aren't memorable, half the time I don't even remember some of their names. The voice acting is good enough for a game like Unit 13 which isn't saying much and there is absolutely no character development. However, since it's a shooter and if you don't care about a story anyways then this will definitely add to your pros list.
Controls:
The controls feel very natural in Unit 13. Tapping the gun icon on the touch screen to reload is probably my favorite of the features because on the Vita, it just seems right. The dual analogue sticks make it feel much like your holding a console controller and that's definitely important for shooters instead of the one stick nonsense we had on the PSP. Sprinting by pressing X works really well and aiming down the sights just feels great.
Gameplay:
This is Unit 13's strong suit. There are a total of 36 missions, 9 Kill the High Value Target missions, and some "Dynamic Missions" where the difficulty and game mode is random. There are many differing types of missions ranging from stealth (a mode to where you can not be detected and killing is not recommended) to Elite (where you only have limited health and killing is highly recommended). It sounds like a lot and it kind of is but the missions are very short and only typically range from 2-10 minutes each (It took me longer considering I tried shooting for 5 stars on each mission and worked carefully to get a high score). This is a perfect idea for gamers on the go because often times those people don't have a lot of time to play long games and Unit 13 separates itself into chunks. The A.I. are pretty decent, they can be dumb sometimes as they don't run to cover and instead sit in the street and shoot at you, but other times they can be tactical as shotgunner's will often rush you. The scoring system can be addicting because you always want to get a pretty high score and when it shows you how far you are on the leader board, you may want to give it another shot and do it again.
Multiplayer:
Very sadly, it does not have competitive multiplayer. (Too bad considering I would have loved to see a SOCOM 2 like game on the vita). Only a cooperative mode where you can play missions with a friend.
Presentation:
With so far what I've seen on the Vita. The overall graphics are not bad at all. Not phenomenal but it definitely doesn't look bad either. The environments could be a little more diverse as the more missions you play, you realize that they recycle a lot of the maps that you play, they just put you, the A.I., and the missions objectives in different places on said maps. It can be a bit repetitive but once again, if this game is played in small chunks, it shouldn't be a bother.
Unit 13 is a solid game that I would give an 8.0 for. This is the average between what number I would rate this game for the on-the-go gamers which is an 8.5 and the number I'd give the others who like playing the vita in general, which is a 7.5. It's a great start to the shooter genre on the Playstation Vita and has a great potential start for the revolution of shooters on portables.
Pros:
Lack of Story (For those that don't want one)
Controls feel great
Can be a little addicting
Characters with special abilities leads to high replay value of missions
Good graphics
Fairly easy Trophies
Cons:
Lack of Story (For those that want one)
No Competitive Multiplayer
Sometimes game can crash (only happened to me once so far)