FFG Have had trouble getting this game back on shelves - their stop-gap solution at this stage was to take French copies of the game and repurpose them for the English speaking market - by adding English language components (though not rules books - which are downloadable).
As for expansions - I have them all and enjoy all of them for different reasons.
Epic - a brilliant way of playing the game, adds an almost strategic element to what is largely a tactical miniatures wargame. The impact this has on the use of ranged units, foot and cavalry is very good.
Call to Arms - An engine for building semi-random scenarios. Very good addition to the game. In fact I think it's a necessity because of the way it allows you to bring in the later expansion units.
Heroes - a lot of fun - if you have an opponent you will be playing regularly.
Creatures - Excellent addition to the game as it broadens the options for using creatures - which are always a lot of fun. Plus the final scenario in that book is very good (though you need many other expansions to play it).
Dragons - See creatures - just a whole lot of fun and well worth it in my view.
The others are mainly troop expansions, all good in my view.
Hundred Years War - Adds some excellent units and is often required for scenarios in later expansions.
Goblins (both Marauders and Skirmishers) add some great units and really flesh out the Goblin units. They have some excellent mounted units.
Dwarves (both Scottish Wars and Battalion) also add some great units - Dwarves have some great musical and foot units.
The three latest FFG expansions - (Horrific Hordes, Bearded Brave and Code of Chivalry) are all very very good troop expansions - they add call to arms cards that allow your random scenarios made through the call to arms system to include units from all the other troop expansions - and add some fearsome units to the game.
There is no real way of playing racial armies at this stage - such as a Dwarf Army or Goblin army - there are stop-gap solutions you can find here - even some officially endorsed, but really - you'll usually be playing a mix of the three races - humans, dwarves and goblins.
I probably haven't helped much - but they are all great in my view. In order of best to the merely excellent I'd have to list:
Call to Arms/Epic - they round out the broader game system.
Troop or creature expansions - creature if you want a more fantasy element, troop if you want more unit variety.
Of the troop and creature expansions I really like the Hundred Years War, Horrific Hordes, Bearded Brave and Code of Chivalry - then the 4 smaller troop packs after that. Having said that I think they are all worth having (though I am something of a fan of the game in case you can't tell).
Sorry - I know it's probably not much help, but there are some short descriptions of what I like about each. If you want more detail you can check out my comments at BGG - I'm caradoc over there.
Oh - and Troll and Country is worth it if you can find it cheap - it adds a Troll which is fun, the scenarios are good - but require a mix of the other troop packs and expansions.
Thanks a lot for the info it is very useful. I had the intention to buy Call to Arms and Epic with the Game...it's a must for me.