I never got the third 4e PHB. What was special about the seeker?
Keeping in mind that I only know them by reputation (having only scanned the Compendium entry many moons ago when I was a subscriber)...
[sblock=Possibly off-topic stuff about Seeker flaws]The Seeker was a Controller, who primarily used bows (though apparently thrown weapons could work too?) Think Arcane Archer, but with a Nature theme instead of an Arcane theme. Unfortunately, WotC decided that the Seeker's path to Controller-ness was to specialize in
soft control, rather than "hard" control. What I mean by that is, "hard" control is where you directly cause inhibitory effects, e.g. a power that Immobilizes, or turns an area into a no-go zone. "Soft" control is where the enemy gets punished for taking additional action--in other words, the way that many Marks get enforced by Defenders is a type of "soft" control ("Don't hit anybody but me, or you'll regret it.") The vast majority of the Seeker's powers go for the soft approach; their damage is good, but their control effects can be easily ignored simply by the monster not choosing to do the bad thing. This, coupled with the Seeker's powers often being "unfriendly" (hurting allies as well as enemies) makes for a character that encourages longer, drawn-out combats with lots of not doing anything.
The other flaw is that, apparently, most of the Seeker's powers rely on zones of Difficult Terrain. Normally this wouldn't be a problem, and in Heroic tier it's usually not a big deal. The problems start to come in toward late Heroic and definitely in Paragon, though, because monsters start getting movement powers that let them teleport, shift, or fly, completely bypassing Difficult Terrain. Your soft-control zone doesn't mean diddly if the mob can just pop out of it via movement abilities.
As a final note, the Seeker is best at controlling a single enemy...which is the place where Controlling generally shines
least, and where other classes often bring in some minor control effects of their own to weaken the Seeker's niche even further. As an example, the original Warlock is almost a Striker-Controller hybrid, and certainly a Striker with a very very heavy Controller secondary role. It is entirely possible to build a Warlock (or even a Fighter!) who is a better Controller than the Seeker is...without sacrificing a single bit of their other role (Striker and Defender respectively).
Anything the Seeker can do, someone else can do better. Someone else can accomplish the Seeker's goals better than the Seeker can, while still doing whatever their class naturally does. The Seeker specializes in iffy kinds of control, and in controlling single targets. When you add all those effects together, you get a lackluster, milquetoast class; it's not a big deal early on, when numbers are smaller and monsters aren't especially flashy, but as levels progress it gets left further and further behind. In that sense, you could call the Seeker the archetype of the "bad" 4e class, as both the Binder and the Vampire followed in its footsteps, though to a greater extent (the Binder is the only TRULY "bad" 4e class, or at least that's the general community consensus). That is, interesting experiments that tried to break the mold but ended up falling short.[/sblock]
It has occurred to me that your question is more about the thematics than the mechanics. In which case, [MENTION=63508]Minigiant[/MENTION]'s response is sufficient, though I'll repost what I said in the block: Think "Arcane Archer" but replace "Arcane" with "Nature/Primal." Communed nature spirits attached to ranged weapon attacks. Kinda-sorta-ish like an archery focused revision of the 3e Spirit Shaman class.
