Coming back after long absence
1. Yes, exotics are very viable.
2. Depends on what game mode you mean. Shields (in most cases) are pretty useless in open world pve and most dungeons, for example. But they could be useful for other things.
3. Ascended and Legendary are the highest tier of armor/weapons. You craft Legendary weapons (and, after HoT raids launch, armor) after doing a long and pricey scavenger hunt-type-thing to get all the components. Ascended drops from champ bags, specific world boss chests, Fractals of the Mists, etc. You can also craft Ascended gear after getting your craft leveling up to 500 in the discipline that makes the armor/weapons you use.
4. Most likely, yes.
5. There are lots. Like, way too many for me to type out here. You could try reading through the old patch notes from when you were gone.
General summary: Living World Season 2 happened, a few balance patches, a New Player Experience (which changed the way you unlock features in the game, how you get traits, and other things), patches reverting some parts of the New Player Experience, the base game going Free To Play (with heavy restrictions), etc.
6. The endgame right now is basically the same as it was before you left. Fractals, wvw, more spvp, crafting legendaries, crafting ascended, etc. People also farm the “new” zone Silverwastes, too.
(edited by RoseofGilead.8907)