I personally enjoyed the last two episodes. I thought the parallel world was an interesting concept - Moorcock's Multiverse and all that jazz.
The cybermen were cool - much better than I anticipated. Lumic, Trig from Only Fools and Horses (I think), was also a good character and one that I felt could have been exploited more. Some ''Mad Lumic Moments'' would have been fantastic - one man in a wheelchair leading hundreds of cybermen over the Watford Gap to oblitorate Birmingham would have a wonderful addition to this story
Sod all to do with the plot, I know, but it would have been fun!
Tennant was good in the first one but not as wonderful in the second one - but then again the second episode will possibly always be my favourite for the one moment that the producers actually listened to the audience - they got rid of Mickey! WooHoo! For one horrible moment I actually thought the Doctor was going to take Mickey and that kid from Byker Grove and CBBC with him. But he didn't. My viewing pleasure on a Saturday night just increased!
Please let them never find this world again - I know it is a virtual impossibility but the producers may decide to make it possible.