The Focus is one of two weapons available to the Elementalist for his off hand weapon slot. The other weapon is a Dagger. Currently, the Focus weapon has a lot of drawbacks, compared to the Dagger. In the next few paragraphs, I want to point out those disadvantages, analyse the skills a little bit and give you some ideas on how to get those two off hand choice on equal grounds again, by suggesting a few buffs.
1. Your choices in Fire Magic
The two skills available are "Firewall" and "Fire Shield". Firewall is a ground targeted area spell that has to be compared to "Ring of Fire". The possibility to put down the wall at 900 range is not a big advantage, as fire fields are most often used in a combo with a blast finisher (e.g. "Evasive Arcana" trait or "Arcane Wave"), so it will not benefit the Elementalist a lot to have a ranged skill. Ring of Fire on the other hand is PbAoE and has great synergy with the #5 skill "Flame Grab", whereas "Fire Shield" offers no synergy effects and is no great source for a might stacking endeavour. In addition: The flame aura effect is probably the weakest of the aura effects. You need to get hit to get the might stacks, which are on internal cool down - and who want to get hit anyway?
The point in this duel goes to the off hand Dagger.
2. Your choices in Water Magic
In water attunement, we have to compare "Frost Aura" and "Cleansing Wave" on the Dagger to "Freezing Gust" and "Comet" on the Focus. Freezing Gust allows you to chill a foe for 3 seconds, which is a pretty good duration and also uses the 900 range category and a cool down of 25 seconds, which is not too bad either. Comet adds a rare potential for a daze effect and is a blast finisher. The problem with this skill is the slowness of execution. The small AoE happens where the foes is at the beginning of the casting time. Should it move with just normal running speed, the comet will most likely miss it. This makes the skill only useful with a slowdown, e.g. Freezing Gust. The raw damage output of those skills is mediocre, so a small combination of the skills will buy you a few seconds time, but only with little effect on supremacy. The Dagger skills offer a good frost aura (from the skill with the same name), which can effect more foes at melee range than the Focus chill skill and the Cleansing Wave is a great healing & condition removal skill that even effects team mates in range.
The point for usefulness of the weapon goes to the Dagger again, but only by a small margin.
3. Your choices in Air Magic
In Air Magic, we have to take a look at "Swirling Winds" and "Gale" and its competitors "Ride the Lightning" and "Updraft". The #4 skills are very different and have both received "nerfs" in 2013, but still "RTL" gets the upper hand: damage, movement and general usefulness makes it superior to Swirling Winds that now is not only unable to block WvW big shots, but most PvE boss attacks at range, too. If you take a look at the Dagger's Updraft and the Focus' Gale, you can see how awful Gale really is: no evade, single target, no damage component, longer cool down and shorter total knock down time.
Without a long discussion, the Dagger scores on this comparison.
4. Your choices in Earth Magic
Earth Magic offers either "Earthquake" & "Churning Earth" on the Dagger, or "Magnetic Wave" & "Obsidian Flesh" on the Focus. While Magnetic Wave is a good skill, with great condition removal, PbAoE damage, a blast finisher and the reflection of projectiles - it has to compete with the AoE knock down of Earthquake that can open up so many other skills, as it usually disables a small area of any non-instant skill use. While Obsidian Flesh makes the Elementalist invulnerable for 4 seconds, you have to ask yourself for what price? Not having Churning Earth, which is the best PbAoE the Elementalist has, with big raw damage numbers, wide area damage and two conditions.
In most cases, you should be better off with the damage option from the Dagger, which "awards" the Focus a 2nd place again.
5. Room for improvement?
Across all attunements, the Focus is a more defensive choice than the Dagger. With the best builds available for the Elementalist currently use "bunker" capabilities with stun breaking Cantrips, there is no real need for more defensive skills in those builds. If you do not want to out-heal you opponent as a bunker, you have to damage him a lot, where the Focus shows another weakness - its bad damaging potential. This is where I would add some minor tweaks: casting times & travelling times of projectiles should either be shortened or removed (at least one of them). Firewall needs to trigger the burning condition on both sides of the wall and not only on the one facing away from you right now. This would slightly increase the area of effect. Both Water Magic skills need a damage buff of at least 25% to make a small damage burst possible and Gale really needs a total makeover. With a duration increase of one second to Swirling Winds, the Elementalist could get a special role again in WvW, which currently is longing for a relief from supercharged Arrow Carts.