My game is currently suffering from bad simulation lag, it improved very little after the last patch, hope they fix that soon. Other than that, I don't have any in-game issues that would make me avoid playing the game. I haven't played with rentals yet, but more because I am not really interested in playing landlord and handyman and I still have enough free lots where sims could live without having to put them in rentals. Also, I read that you don't see the neighbours using the amenities in the shared spaces, so there really is no incentive to move the sims into rental lots. As for bodyshape changing, all my played sims are growing fat eventually, didn't know that was a bug, I thoght it was just the way I played them. Every once in a while I take them to the restaurant and let them eat diet ice cream and they go back to their slim shape. With some I tried keeping them in shape with exercise, but I noticed they need to to do that everyday or else it doesn't work.
I don't play the game often, so I am not sure about bad simulation lag. But to think again, it's lag lately when there are many sims in the same lot.
I haven't tried rental because of the same reason as you too. Not interest in the gameplay and I still have plenty of free lots to use. Unless I want to play in a world that lacks of normal lot. (I'm thinking about Del Sol Vally as I am playing with the celebrity.)
About bodyshape, that's why I separate bugs and features. Bodyshape changing is the feature from the start, not a bug. It makes dynamic and reality of the game. But it's too effective sometimes with the community lots that make people eat repeatedly (and this seems to be fixed now or in the upcoming patch). Bodyshape changing is a game-breaking for people who want to take the story screenshot seriously.
Exercising has some side effects too if choosing weight training. Muscle value will change too. Moreover, it's not like TS3 that the bodyshape will go back to its original shape over time. It's too much work if you want to keep all of the population have their original body "without mod"
