I thought the backgrounds looked amazing. Particularly the night sky with all the shining stars on the Vita's OLED, but probably not if you already played the Wii game otherwise yes I'd say it was worth playing for $20. Although you could also get full AAA console games for $10-15 right now so it depends on the person.
It is a tough platinum trophy since you'll have to collect all the swords in one run, do a speed run in another run and do a final run on the insane difficulty. It was fun to mix/match and play around with all the swords. The game was pretty much about exploiting and cycling between the swords overpowered special attacks. The cyclone type blades are the best for conserving your special meter to build up more meter on the other 2 of your weapons you swap between but certain blades all have their uses against different bosses. Overall theres like over 100 blades to collect, but some of them are more powerful versions of previous ones.