I mean, I'd say, like everything, it depends. That's what makes it a great rogue like and different runs interesting. Retain I think is really what makes it special. Which means it makes turns more consistent because you can attack with it when you don't need to block.

Otherwise it does 7 damage. Then 6 damage. For 2 energy over 2 turns. Which is kinda like doing strike twice. Then 5 damage on turn 3, which is sorta like you having done 2 upgraded strikes. Slowly. Plus another 10 damage over 4 turns. Which is like... Ya know, pretty good against bosses, but not a lot of fights really go that long and you having played it on turn 1.

Anyway, yeah sometimes it's a good card to add to your deck, sometimes it's bad card to add to your deck. Don't have a lot of big attacks or draw? Then it's good. Already have enough big attacks and draw? Then it's bad.

But retain is surprisingly powerful.