For me 1, 2 and New Vegas are the best (all developed by Obsidian/Black Isle). I don't like The Bathesda ones that much (3 and 4), but they're still good and entertaining. The multiplayer (Fallout 76) I never tried, and probably never will, and Tactics I played just a liitle bit, maybe a few missions.
I still would recommend you New Vegas the most, you can play it as First-person or Third-person, the roll-play is great, multiple dialog options, multiple endings, super deep leveling system with a lot of options, interesting quests, open-world, non-linear, great-looking armors and weapons, superb soundtrack, and I can't stress this enough - MODS.
The last time I played it was when corona started, I finished 100% achievements on GOG, and I did it on the hard difficulty. It was a blast for me, I enjoyed it very much and I still remember it fondly. But, I guess it all depends on personal taste. Maybe watch a few reviews on youtube and decide for yourself.
RPGs are my favorite genre, but I played a lot of isometric stuff, I don't know if there is anything else to recommend, beside Dragon Age and Mass Effect that you've already played. Star Wars K.O.T.O.R. 1 & 2 are one of my favorites, it's third person but it's kinda old-school, with D&D leveling system, predecessor of Mass Effect, developed by Bioware (and the second one by Obsidian).