wow, 2pack slumlord advice ftl
bandaiding the problem on a home that you own, really?

tile is great if you know what you are doing, but for an inexperienced person its easy to end up with cracked tiles in a yr when you add heavy objects with small footprints that vibrate on top of them, there are strategies to avoid this of course and if you plan accordingly shouldnt have any issues, but on an uneven floor in a high foot traffic area with lots of sharp heavy pointy things to chip and crack away at it, is it the best option in the first place?
i would still do tile though h: just think ahead (tile size thickness etc...)

as far as wtf is going on under there, are you saying that it is two different cement pours that make up the subfloor?
or part concrete part something else framed out?
whats the wall foundation like?
im confused