Gameplay is turn-based, and I love it. You'd need to strategize your attacks (especially for the harder quests), but what I like about this is that you get to enjoy the gameplay in different ways - you can simply enjoy flexing your favourite/strong characters in Co-op with other players, or waste your brain juice planning your strategies and teams for those frustrating Lv 180 quests. My personal favourite kind of quest is the COSMOS Lv 150 kind, since they pose a fair amount of challenge and yet aren't as troublesome as CHAOS Lv 180.
I'm quite fond of the storyline as well, I really love the 'all-star' idea going on. Act 2 onwards has been really interesting for me so far! They regularly have events introducing new/old event characters and I really love farming Gems from them too :P
As for the gacha... The game is very generous with free Gems, you can save A LOT of them as long as you have the patience to accumulate them. After all, you really need patience if you want to guaranteee getting something you want from the banners. That's at least 75k Gems for one EX weapon, and 100k for a BT. I'm advising this based on my own experiences - please don't trust luck, just save and be safe You will definitely have lucky gacha pulls every time now and then (10% for 5☆ is honestly really good for a gacha game IMO), but just save those Gems if you don't want to end up getting disappointed. Just whack those Draw Tickets if your hands are itchy.
TLDR: Nice graphics, awesome music and pretty entertaining story and gameplay. Gacha is nice to you as long as you have the patience and self-control to save your Gems.