Roland use different technology from Yamaha. Yamaha use samples whereas Roland use software generated sounds. You would think that this gives Yamaha the edge for acoustic drummers but Roland are more popular. I guess Roland spend more on R&D and have some excellent hi end products. Ther are companies that sell Roland compatable kits for download onto your TD6 and upward models. These downloaded kits are very good and do sound authentic. I prefer the compactness of the Roland kits and the general feel of them.
Comments about hihats and cymbals. It is undoubtedly true that the biggest difference between acoustic and electronic kits is the cymbals and the ride and hihat take the brunt of this criticism. The hi end Roland VH-11 and VH-12 hihats are better than the other lower models but there are so many nuances to an acoustic hihat that it clearly is difficult to simulate. Nevertheless the VH-11 that I have has a separate and floating upper hat, and it has edge and main section sensitivity. The hihat opening also has a few steps between fully open and fully closed. Thus, there are still a lot of tones that can be generated. The ride is possibly slightly less an issue with rim, shoulder and bell tones.
What isn't often said though is how much fun they are. If you suck they are fun as you can play along to built in tracks or any external source. It has a built in metronome. You can record to the module and listen back (to check how much you suck). All with the push of a few buttons. The biggest plus for me is being able to play at any time. Otherwise I would never get the chance to practice. They are excellent for doing recordings as well, as you can record to midi, correct your mistakes (or mine) and then choose other sampled sounds if you want to change say the snare etc.
E-kits get a lot of stick from acoustic players. I'm not defending the cause per se, but they work admirably for me.
Davo