Its up to you :), I played Shogun and MTW/VI for insane amounts of time in MP and like you I thought Rome was dreadful and stopped playing MP. I own and have played every TW since in SP and from a SP point of view they have been steadily improving.

When Shogun 2 was announced it re-ignited my interest in Total war again and I started playing NTW online, I'm currently trialing with Aggony.
I'll be honest with you I don't like the era much and I don't think its particulary well suited to TW games but having said that apart from not having a chat foyer I quite like it.

I'd imagine the basic control and game mechanics in NTW will be close to S2's so its good practice for S2 and the single player game is pretty good. Try the demo :)