In preparation for our next major campaign, I am strongly considering using the 2nd Edition Pathfinder rules. The setting obviously is familiar to the group, and the ruleset is similar enough to make things understandable. And since they have a full campaign of experience now, it would not be too challenging for the group to create their own characters from the start, rather than using pre-made options. My only concern is changing the rules midstream – the current set is considered a playtest version – and most likely will still change quite a bit before the release next fall. But even if we only play a short campaign, it would feel like a whole new game.
The other alternative I have considered is going back to my home-brewed version of the Rolemaster mechanics – something I have referred to in the past as “Pathmaster”. It is tuned heavily to mimic the setting and feel of Pathfinder, but with the detail, realism, and deadliness of Rolemaster. Unfortunately, it is a rather number-heavy game, with lots of calculations and math involved. None of it is too complex – fractions, percentages and adding – but it is easily overwhelming for anyone who is not a math-gamer. The system however has the advantage of being very detailed – you really feel the grittiness of the combat and world – and it has always given me much more of a Lord of the Rings epic feel, compared to the more abstract Pathfinder and D&D mechanics.