Something exists: I find it odd that something at all should exist. I am conditioned to think in a cause an effect way, so I think that an eternal first cause could make sense and might even be necessary.
It is not odd. If nothing could exist, you wouldn't be here to ask the question. This is like the question some people have about the expanding universe: if nothing can travel faster than light, why does the expanding universe not obey that law?
The answer is that those objects don't travel faster than light
though space, but space can do whatever the heck it wants. In the same way, nature can do whatever it wants and does not need some superhuman (god) to do so.
In the end it's all just particles that exist. Apparently those can exist. Add enough of them together in a suited environment, and you get life.
BTW, how you are conditioned to think does not matter. You are not evolved to be conditioned to understand quantum mechanics for example.
Experience: It seems odd to me that experience exists in any form at all. it doesn't matter how it happened, but that it exists is enough to cause suspicion.
What do you mean with experience? I guess my reaction underneath also applies for this.
Good things exist: This is subjective, but things are still good from a subjective point of view. Happiness, love, purpose, feelings of rapture and wonder etc. They all exist. If they are false and illusory, it doesn't matter. If they evolved for other purposes, it doesn't matter. The fact is these things exist, and this causes suspicion.
Side note: Bad things exist
Bad things existing do not erase the good things. The fact that good things exist still holds, and the suspicions that I get from those good things still hold. I take my entire personal experience at face value. I understand the experiences of others might not be as pleasant as my own, but this doesn't erase my own experience, and the fact that good experiences exist leads to suspicion.
The existence of good and bad things is because of evolution.
Good: surviving, reproduction
Bad: the 'survival machine' (= animal) getting injured, dying
Everything is a consequence of those principles.