| Mnemon |
Selling a group that has been playing 3.5 for an extended period of time (I was an early adopter of 3.0) is a difficult and time consuming task. It won't happen overnight. It the case of my gaming group it probably wouldn't have occurred at all if we had not had access to leaked core rulebooks (we all have since purchased many a 4e product).
In my gaming group, we played the Games Day adventure and Keep on the Shadowfell pretty early. Those experiences left a bad taste in our mouth, but not necessarily a hate. So we tried some more sessions with homebrew starting at first and then a short story arc with paragon level characters to see what that would be like. This experimentation occurred over a six month period of time.
The only specific concern you expressed was about combat and powers. 4e definitely is different. The speed of combat will only get better with experience. Once the character become more familiar with their powers and let go. The amount of decisions to make can seem overwhelming to someone coming from 3.5 where the only decision for non-casters really is what do I swing at. People who play casters in 3.5 tend to have less trouble switching. Power cards help.
The greatest advice I had for my players to speed up combat was to let go, have fun, and relax. The 4e system was built in an extremely balanced nature (to the extent some don't like the balance). Some decisions are better than others, but ultimately rarely is the choice to choose one power over another game breaking. In my experience, the difference in optimal and sub-optimal in 4e is at most 10-15%.
Ultimately I as the DM came to love 4e and would go back to 2e before I would go back to 3.5. The players have come to enjoy it as well and when I had to leave for an extended period of time and they started up some short pickup games, they were all 4e. This is from a group that is heavily invested in 3.5 (I have all but a handful of the WOTC 3.5 books).