I am finding my expert summoner play through very, very hard. I have died over and over, and over again. Maybe it will become more fun once I have better gear (currently have meteor armour and space gun) but right now its just annoying and makes me want to tear the flesh off my face and the hair from my head. Enemies do so much damage that you can only take a few hits. You are forced to stop whatever you are doing (like mining) to deal with that annoying bat or slime, or worm. In normal mode, you could just continue mining and kill the enemy with your pick while doing so, but since they have more health in expert mode, you have to get out your weapon and deal with them.
The thought of constantly being killed by queen bee to get the hornet staff is horrible. I just decided to skip it by getting my hands on a reaver shark and going straight to hellstone for the imp staff. Hell is proving to be quite a challenge. Its almost like the game senses when you are building or mining, and increases the spawn rate of lava slimes and fire bats. I know that when I go down to hell, I will only have a few minutes to mine hellstone, because enemies are so damn strong.
Overall, expert mode is very frustrating, and progression is difficult. For me, the thing that makes it so hard is that enemies have double health and are stronger in their attacks. It really does make the early game frustrating. Zombies for example, can sometimes have melee weapons. 3 or 4 hits from those, and you're doomed. It also appears that enemies "home in" on you more in expert mode, like slimes jumping up at you right as you jump. In normal mode, their jumps were predictable.
You cannot afford to be clumsy in expert, or you WILL die. There is very little room for mistakes.
