Have never played it...care to give me the rundown?
At it's heart WHFRP 1st ed is a percentile system. Attacks and skill rolls all made on d100 and checked against weapon or ballistic skill or a relevant attribute.
It uses a career lifepath system and players roll their starting career randomly. No starting career is glamourous but some lead to more promising careers quicker. A career will offer a range of improvements to attributes, skills that can be taken (each improvement costing 100xp) and details what moves that can be made into new careers (100xp to change).
So you might start as a rat-catcher and spend some time taking a bit more weapon skill and a boost to dex and some resistance to disease before deciding to move on into something else, which offers different improvements. Starting careers are suitably grim - beggar, rat catcher, smuggler, apprentice, footpad. Advanced careers are suitably gritty - templar, witch hunter, assassin, spy, those kind of things.
I don't recall much about magic as I didn't play the party wizard. But it's essentially like early editions of Warhammer - four levels of Wizard spells and nothing stupidly overpowered. There's no quadratic spellcaster problems, and we had no problems playing with a predominantly martial group - magic is not the presumed solution to the party's problems.
Most characters will start with between 3 and 6 wounds (HP). Weapons do 1d6 damage, and sixes explode (roll again and add, and keep going until you stop rolling sixes). Dropping below 0 wounds means you start rolling on increasingly nasty criticals tables to see how badly it messes you up. The -1 table is survivable. The -6 table ranges from a variety of permanently crippling injuries to instant, messy death. Combat is brutal, rather than attritional. If you hit something and it stays standing... you get worried fast.
The world, as envisaged, is a dark brooding fantasy Europe of mistrust and superstition, chaos and corruption. The original
Enemy Within campaign was really, really good. But the scenarios which comprised it are hard to find and very expensive now.