If you take the Shinkansen from Tokyo to Sendai you spend a fair amount of time in tunnels. There are some pretty spots along the way but you wont be missing anything that you can't see elsewhere (farms, industry trees, etc.) It's not an unpleasant trip but it's not remarkable like the trip from Tokyo to Osaka where you can see Mt. Fuji on a clear day.
The shinkansen and local trains between Sendai and Tokyo are quite scenic (not super stunning like some other places I go, but worth looking at), but you get smilar scenery in other parts of the Kanto plain area. I have had feedback from guests that they like the contrast between the leg within Tokyo out to Omiya and then up to Utsunomia (for day-trips to Nikko) or across to Sendai.
I find the scenery in that area better than something like the Tokaido shinkansen route (also with tunnels), and quite enjoyed a trip I had last year between Sendai and Fukushima on one of the local trains because it did cover a different route to the shinkansen.
Depends a bit on what other legs you are doing on your trip.
The Tohoku Shinkansen (as much as the Tokaido Shinjansen) go through sound barriers in the cities and through tunnels in the countryside. There are a few nice parts along the way, but it is not a very nice countryside view ride like the Tohoku Line (or the conventional tracks; I particularly like from Kuroiso and Shirakawa northward as the scenery clearly changes to that of open and wide Tohoku Region).
As mentioned above, Yamagata and Akita Shinkansen run through very nice scenery as they are just former conventional lines with widened track gauge to allow direct trains onto high-speed Tohoku Shinkansen. Yamagata Shinkansen is an old curvy Ou Line reuse which goes through the Itaya Pass along river gorges. A documentary of the Itaya Pass: https://youtu.be/fGoc_FB0cYAEdited: 19 May 2018, 10:27