The hold position and hold formation buttons seem to have been condensed to make way for the special ability button. In STW/MTW the idea of Hold Position was to stop units chasing routers and return to their positions after winning a battle. Hold Formation was only useful for spearmen when forming up to absorb a cavalry charge or defending a position.

If you have a group of high attack and low defence axe infantry or cavarly that you're using in defensive role as flankers, it makes sense to place them in hold position to prevent them from straying, but no sense at all to place them in hold formation as this will seriously hit their offensive ability.

I can see no reason why the original two separate buttons could not have been used.

My other annoyance is with the "classic interface" (the STW/MTW style Minimal UI) for battles. In RTW (not sure about M2TW) this autohides itself which is unnecessary. It would be better to have it always visible. I found that when clicking near the horizon to order a unit the interface would keep popping up instead, forcing me to reposition the angle of view.

The right click pop up menus are also a feature that I miss. In STW/MTW you could right click on a unit to change it's order, formation etc instead of using the top interface or keyboard shortcuts. It's nice to have alternatives.