While certainly playable the amount of crashes and other issues will get to anyone eventually if exposed to it for long enough periods. If all goes as planned the engine upgrade should result in a more stable game (seasoned with lovely new bugs to sort out). A dropping player engagement is quite normal in instances where as early alphas as ours are being tested by backers.
I'd be interested in hearing from the "waiting for new content" crowd as to what exactly they are waiting for. It can't be new game systems (like the formation buff systems) nor can it be new units or skirmish areas - cavalry or artillery perhaps? They are going to be waiting for a long while if that's the case.
- Trusty