When I played lockdown, a long time ago, before I realized that 4* knights are not welcome in tier 3 and get totally trashed by wolves clones, expert gunners, and pro bombers alike, I gravitated towards the guardian class. I was not good at handling the speed of the striker, and did not have a flourish myself, so I wanted to play defensive and support my comrades. Sometimes it went well. Strikers and Recon came to me for healing, I stood near fights to give my pals a defense boost, and fended off some attackers where I could. But most of the time, I ended up trying to hold my own, unable to run away, against an onslaught of strikers. Not a happy experience.

These are MY issues with the class:
1. You have no evasive abilities. This is likely because of the amazing shield and defensive buff, but if you cannot get out of a brawl, you are basically dead, unless you can SWING YOUR SWORD fast enough to get some damage on them and scare them away, or hold out until someone can help you. Maybe I am just a horrible LD player, but oh well.
2. The healing rate is quite slow. Speeding up the healing rate would however be too powerful. Perhaps a different ability?
3. This is sort of a general con. Getting hit interrupts your own attack. This is clearly there for a reason, and I expect no change, but remember these are just my issues. It was also probably a mistake to use jalovec...
4. The shield brakes very quickly. Maybe just a small health boost would be helpful. Or a change in a particular mechanic. Instead of shielding allies completely at the cost of shield health decreasing quickly, maybe the shield should only improve the defense of the ally while still completely protect you from harm.

Now how about recon?
I actually think this is a great class. You get a health boost, invisibility, and can mark players for death. Nice. Also, because the class was "buffed" recently, it will make Recon a great competitor with Strikers. I do not see anything wrong with recon.

Striker:
Blindingly fast swordsmanship. <-- accurately describes the stereotypical striker, imo. They whip around you, hitting you at every angle before you can turn your mouse fast enough and hit them back. Scary. Swords do more damage, especially with wolver sets, and you get an attack speed increase. Most stickers use flourishes/BTBs, which are already fast and powerful. Some even have amazing UV's that assist them. The health penalty is not the most significant change, but compared to the other classes' health boosts, it can get you killed in less than a second if you are not well-practiced.

Overall, Striker is best for swords, but takes practice, Recon is good for bombers and gunners, and Guardian is for those who don't play lockdown all that much and do not get practice. Guardian has very basic and easy-to-figure-out abilities, but it just does not compare to the sheer numbers of strikers that can dispatch you in a second.
This was solely from my experiences in LD. Care to share your issues/preferences/snacks?