With a sale right now on RPGNow of 25%, do you think it is worth it to get 1st edition PDF for 7$?
What are the major improvements/changes that came after in the succeeding editions?

There are a number of important differences between 1st ed and ed 3, 4, 5, 5.1; the latter are more or less the same game, but 1st ed have - among other things - a different Glory-system and a different skill set. If you can live with that, I guess you should buy it. Otherwise go for one of the later version. (Note: there is no 2nd ed).

Well - I like 1st edition better than all others. Here are the differences between 1st, and the later editions, that I can remember

1) Skills can not be improved beyond 15 except by checks or Bonus Glory points; in 3rd and higher, you can spend 1 pt in the Winter Phase to boost a skill over 15
2) Glory awards are much lower; no points for Traits of 16+, 100 Glory instead of 1000 Glory for knighting, you can lose Glory, while in later editions you lose Honor instead (a new passion)
3) Battle system is beautifully abstract in 1st edition, but not very flexible; Battle skill is not that important in later editions, but player actions become more pre-eminent
4) There is no Armor of Honor for being Chivalrous; Religious bonuses are smaller
5) Character generation is random in 1st edition, more point-buy in later versions
6) 1st edition is less fleshed out then later editions, which have awesome background source material

Yup, that’s definitely a bunch of things that later editions have done better. ;)

(Also, language skills.)