I own and have watched all of TOS- R. My verdict? Thumbs up. The new effects are just icing on the cake. The stories remain intact. I liked things such as the Romulan Bird of Prey in 'The Enterprise Incident' and the D-7 fleet in Errand of Mercy.
It just adds a bit of flavour, thats all. And you can always watch the original versions on Blu Ray if you don't like the new effects.