I, Borg was an interesting take and a nice look at what exactly it was to be in the Collective. Granted, its attitude of the Borg was pushed aside by the later development of the Borg as being assimilated from other races, but at the time, it was a different view, and I liked it, especially given that it was intended as a more thoughtful episode than the previous ones, and had a facinating moral decision - where is the line drawn, do you wipe out an entire race just to protect your own?
Descent Part I was a 'hold on to your seats' ride. Opening with the Borg massacre, an open and running phaser fight between violent and malicious Borg and the Enterprise crew, including Data feeling emotion, and violent emotion at that, up to the point of admitting to being willing to kill Geordi in order to feel it again... It had great potential.
And then they bring in Lore and Part II happens. It reduces the Borg to nothing but a handful of Mooks and focuses entirely on Lore, and while I like seeing Brent Spiner play someone other than the eternal straight man, I hate the whole evil twin thing. Maybe it wasn't as played back when they introduced Lore in '88, but now? Cliched as HELL and epically played out and tiresome. And Lore is the important part of the story, that's the villain of the piece. The only things I enjoy watching in the second part are the Beverly in command pieces, especially when she brings up the metaphasic shields from her own prior focus episode. It's nice to see her used in a command situation, showing she can take command if the need arises.