Having travelled on both QE2 and QM2 almost the same number of times, I have two dislikes. QM2 is too big, we have met fellow passengers early on in our trips to never see them again, whereas QE2 was just the right size and one would often meet fellow passengers from earlier in the trip several times more. Also, QM2 is much more obviously commercial (Canyon Ranch, extra surcharge dining options - however she has more dining options). It should be pointed out QE2's Lido had themed nights (such as Indian with the relevant chefs) whereas in QM2's equivalent the King's Court these themed nights are extra surcharge dining options (albeit slightly more upmarket). I like QM2 but QE2 will never be replaced or matched due to her uniqueness. Having said that QM2 is unique in her own way too. Finally QM2 isn't quite as happy a ship (crew cuts, larger ship etc.).
Having said the above I still love QM2 partly as she is the only Ocean Liner left in active service doing what she's designed for. Also she is very imposing and magnificent (including her funnel when onboard), the largest Ocean Liner ever built.
Thomas