The gameplay in ESO is similar to the single-player games. Quests are far from the kill-20-rats, collect-50 spider eye slog present in so many MMOs these days, with actual interesting storylines rather than timesinks. Major features are still being added with every patch. The last major patch pre-B2P added the justice system so you can steal and launder goods, or get killed by guards in failed attempt. I actually like ESO's graphics better than Skyrim's because there's actual color, not just gray, white, and brown. It even runs well on old computer systems, mine being 8 years old and running at 25-35FPS on medium-high settings. It has a diverse crafting system, with racial styles and rare styles, always popular items for auctioning, and the graphics, did I mention the graphics, will draw you into the game. It caught a lotta crap early on for not being a WoW clone or not being simply multiplayer Skyrim. There were bugs - an armor-ability combination that allowed one to run at horse speed in sneak, occasional lag in pvp post-major patch, cuz the best way to test a game is to put 80-100 players together and a fortress between them to fight over. But these issues are few and far between over a year after launch.
There are enough similarities in this game and the single-player games to make a smooth transition and, though there is an item shop now, it is not pay to win, only selling largely cosmetic items such as pets or mounts, or food and potions that you can pick up for a few gold anyway. PvP can be played casual, but if you get hooked on it and get running with a good group of people, it will be hard to pull away as you carve out a piece of enemy territory. Ranged builds, liberal use of ballistas can be the safest bet but it can be just as fun to play cleanup as melee while the ranged players rain firey death on crowds of enemies from a distance.
Coming down the pipe soon - several new armor styles to come with the opening of the Imperial City for pvp, currently blocked off by hordes of daedra and destroyed bridges. This along with the assassins guild and with it the possibility of a somewhat limited pvp system in the standard game - people will be out to capture bounties - oh, and spellcrafting - will add even more variety to a game that, like the single-player ES games, you can already play almost any way you could imagine and do well.