While it is not a dramatic overhaul, personally I liked the changes in version 2 a lot since they ironed out some problems I had with 1st Edition. Original Traveller feels like a simulation created by computer scientists. Mongoose Traveller 1 essentially kept that feeling with some adjustemts. Mongoose Traveller 2 strays away markedly from OT in several places but this was clearly done to improve the rules as an RPG.
My favourite changes are the way stun weapons work (they were clearly OP in MGT1) and the simplified stats for animals which makes things a lot easier for Referees and also removes the strange effect of a dinosaur-size creature having negative DMs of -6 or more when they are only moderately hurt.
Also it is now clarified what your characters can do with their ship shares or benefit starships when the campaign is not designed for starship owning Travellers.
Having Hit Points for ships is also a more straight forward way of handling space combat.
Mongoose did a great job of fixing all the problems I had with MGT1.
The only thing I dislike is the general Science skill that is simply not plausible. I think they went overboard and oversimplified this. Mongoose seems to agree with me since the Traveller Companion has an option to use a middle ground between V1 and V2 science skills.
From a graphical design POV MGT1 and MGT2 are night and day. MGT1 uses crap drawings dating back to the seventies. I don't want to attack the artists but standards have evolved in the last 40 years. MGT2 has high quality graphics that add a lot to immersion. This high standard is very consistent and applies to all products of the MGT2 product line. While MGT1 only had few, bad illustration, MGT2 has an image for pretty much all (!) items, ships and major NPCs. Very good stuff!
The only drawback here is that again they went overboard and decided to include flashy isometric deck plans, which are absolutely unusable if you want to have them as printouts for miniatures or graphics in VTT. But again Mongoose seems to backtrack and newer products, like the 2022 update of the rulebook, went back to 2D deckülans.