I've beat the game once in veteran and I'm currently at my 2nd run on professional. Haven't played online CO-OP and I gotta say this game is actually a good game. I believe that you would enjoy it. Being no fan of the RE series yourself, you can have a fresh experience...though you might be lost at the story (names, places, events).
And the achievements are quite easy to unlock, but one or two require certain time. There are no online achievements, so you can unlock all of them by yourself.
XBox 360 Gamertag: Rol X box360 PSN ID: OvO_Nyctea_OvO
Veteran is a fairly challenging. I assume Professional is hard. I actually skipped professional and jumped straight No Hope Left (co-op required)... Jesus that ****'s aggravating.
But like someone mentioned, this game is best experienced with a co-op partner. As a single-player experience I gotta say it's a lengthy and fun game full of content. You'll also find some time challenging yourself in Mercenaries.
MFW I passed SS http://aftershockcipher.deviantart.com/gallery/?catpath=scraps#/d4hajdo