Linear can be good. Let's compare PS2(ultra sandbox non-linear gameplay) to PS1 linear gameplay.
http://oyster.ignimgs.com/mediawiki/apis.ign.com/planetside-2/thumb/d/db/PlanetSide2_2012-12-06_10-57-01-85.png/468px-PlanetSide2_2012-12-06_10-57-01-85.png
http://www.planetside-idealab.com/images/commandmap_commenu.jpg
Here we can see in PS2 battles are far too stretched out, less participants because there are too many territories and the hex system encourages you to, rather than fight your enemy, go around them. In PS1 battles are much more focused, participants are funneled towards objectives and zergs clash head on. Linear is not always bad, as long as it is designed right. In ps1, there were always a 3 or 4 potential targets along with the possibility to back-hack behind enemy lines.
i know about all this, PS1 had bottle neck spots for a reason, due to the facts that the devs wanted heated battles with a lot of hardware, also they wanted big base battles with 200vs200vs200 players (had that many times but never actully had 200+ onscreen at the same time, 100+ yes, but not close to 200.
played PS1 from day0 to almost end.
TESO will have gateways like DAoC had long time ago, gateway fortifications in strategic locations, and those will be every now and then a bit of a hotspots. But i am pretty sure that there is more open areas in Cyrodiil, and thus gateways prolly r small fortifications seperating the different areas, but avoidable prolly.
i personally feel that Cyrodiil will be very open area.