A couple of my observations and experiences:
I agree with you, cruising can be expensive. However, not any more than flying to a destination and staying there in a hotel. The question is do you like cruising enough to pay for it. We love it...so much so, it has it's own separate line item in our family budget.
You can control the levels of tipping. They are not set in stone. We pay for good service and reduce the tip if the service wasn't very good.
The main dining room food is not a five star restuarant. We are foodies and would rate the food at 3.5 to 4 depending on the cuisine that day. That's still pretty good. The Windjammer is your typical buffet with that type of quality of food, ableit with a nice variety.
I agree, hot tubs and getting deck chairs are sometimes hard to come by on the ship. This can be annoying. I wish the Royal would more agressively enforce their 30 minute rule. This rule is suppose to reduce the "saving" of deck chairs.
Our kids (ages 10 and 17) went to the kids activities and had a blast. This was on Liberty of the Seas. I'm not sure if Mariner is any different.
I think the work out facility is at or near the same level as your typical gym... Except, the cruise's facilities have much better views out the front of the ship!