The principle behind the 'Skeptical Shielder' build is based on my savored experiences with games that allow the player to possess overlapping spheres of destruction. Fully outfitted, you can transform both you and your allies into an offensive DPS nightmare for your foes.

Tier-1 causes Lightning Shield recipients to be stronger attackers, always a good thing and even moreso when they are heroes, and as it is the go-to spell for this build you gotta have it.
Tier-2 causes Lightning Shield to last longer and cost less to cast so it is a must.
Tier-3 causes Lightning Shield to imbue a free damage shield (ala rune), and that means Rehgar has partial Tassadar capability. Sadly other Tier benefits to not delay it until the shield activates (ala Tier-5) so it's more useful once combat is going. Still, an extra combat rune (for you and a friend once Tier-6 is online) isn't a bad thing. There may be something else in Tier-3 you prefer more, but I didn't find anything I liked better.
Tier-4 is a supreme ally booster, turning all nearby heroes into a 10-second kill squad.
Tier-5 decreases the recast time and holds shield activation until enemies are in range. Once this happens the battle is getting close to being over.
Tier-6 causes a cast upon an ally to shield both you and the ally. You could feasibly skip this Tier, but I don't recommend it. Then a single cast on a nearby ally mid-combat allows you to hit a nearby enemy between you with two Lightning Shield bubbles in one heartbeat.
Tier-7 is an insane enhancement of Tier-4 -- now ALL allies (even non-heroes) everywhere receive the killing benefit. By this point in a battle I frequently run with my allied heroes in a squad, and when we meet three or more enemy heroes we usually kill them all while only losing one or two (an excellent, game-changing trade when the respawn timer is 50 or more seconds).

The build may not seem like much looking it over, but I have high success using it. Ponder for a moment the effect of running with a squad of even basic soldiers while casting upon each (note: after Tier-5). Each then has a damage aura that auto-activates when they enter close-combat, and they run right in and cut enemy target(s) to shreds -- consider the overlapping lightning shields of destruction on a squad, an enemy hero, or really whatever. Add the benefit of you joining in to support the onslaught and the effect can get downright silly.

You will no longer need a map effect or allied help to remove an entire emplacement of defenses, you can make it happen solo.

Squad of heroes attacking you with other heroes nearby? Great! Get everyone together and activate Bloodlust to show them why it was a really bad idea. After Tier-7 you can simply watch the map for an opportunity when many of your allies are in combat.