It's pretty easy for me to slip into a long paragraph raving about "The Invasion." It's my favorite Doctor Who
story ever. Tobias Vaughn is such an excellent villain, and I love it whenever he starts berating Packer. The 2nd Doctor, Jamie, & Zoe are among my all-time favorite TARDIS teams ever, and Isobel Watkins could have easily been an excellent companion in her own right. (I keep hoping she'll show up on the new series sometime.) Plus, it's the frickken Brigadier & UNIT!
And I really liked the animation work done on Parts 1 & 4. On the one hand, they weren't able to quite capture the nuances of Patrick Troughton & Frazier Hines' performances. However, the animation actually makes the story look better as far as the variety of camera angles, more frequent cutting, and the generally more noirish feel.