Theres definitely reasons and ways to be tactical in this game, it just a great deal different from DAO. Ive found mobility and flexibility to be key since very few fights allow you to take a defensive position and funnel your enemies towards you.
I love and hate the enemy waves at the same time, it keeps the battles interesting but can totally fucking end you if youre not careful. Poisons and bombs I have found are super important, especially later in the game to help deal with groups, as are rogue skills like stealth, chameleons breath, evade, armistice, back-to-back and others that help move your weaker characters away from mobs, reduce aggro and so on. Mage skills like Barrier are even more important to keep holstered for an important time and Merril's Stone's Throw ability is great for getting her out of an unwanted scuffle.
I find myself conserving my abilities a lot more, where as in DAO it was pretty easy even on Nightmare to just set up your group right and just unleash everything you had in an orchestrated barrage and the battle would be over in seconds. Now though I have to hold out a lot more to try and do the most I can without using my big guns and Im far more conscious of my cool down times in order to plan out what I can use now and how soon I can use it again for the next likely wave of enemies.
I havent tried nightmare yet, probably will on the second playthrough, I imagine that will be a great deal more difficult than hard because of FF, but Im interested in seeing how I will fair and if I can keep my group alive.