"It looks fake" is a common critique from someone who has observed an aikido class. Traditional practice looks like the person being thrown is cooperating, and in many cases they are. There's a reason for this. For example, if I'm training with a newer person, they may be still trying to figure out the body mechanics that make the technique work. They will learn nothing if I lock up and don't let them do the technique. The basics of Aikido require a combination of movements that need to be integrated into the whole. A common thing I hear from newer people is "There's a LOT going on here!" even for very simple techniques. There's no sense in trying to do this with speed and power if you can't do it slowly.
As the practitioner gains experience, he can increase his speed and power -- assuming his training partner has the experience to absorb that speed and power without injury.
When I initiate an attack in Aikido, I'm lending my body to the other person to allow them to practice the technique. The training environment is controlled to allow the practitioner to practice the technique at hand. Yeah, I could move in such a way as to prevent the technique from working, but assuming an experienced partner, he will then just do a different technique, which is not what we're practicing (example: on my last test, I vapor-locked on an incoming attack, and for a moment totally forgot what technique I was supposed to be demonstrating. The attack kept coming, so I automatically responded with a tai-otoshe throw, instead of the kaiten-nage ura that I was supposed to do. In a way, that demonstrates a certain level of proficiency, because I reacted without thinking, even if it was the wrong technique.) As you become proficient in the basics of the techniques, you can start playing with them to see what works best.
On resistance: Resist Aikido at your own peril. Most injuries are self-inflicted. Aikido techniques are designed to control the attacker, and their resistance is what will cause pain or injury. If I see an opening with an experienced practitioner while being thrown, I will exploit it. To not do so would dishonest of me. I'm known for being hard to pin, and I help my partners learn how to close the holes that keep me from being pinned. Nikkyo can sometimes be like picking a lock to get the joints to work for the take-down. I can resist and allow my partner to figure out how to pick that lock, but when I do so I have to be careful, because the natural respose to resistance is to try harder, so when that lock does get picked, it's going to happen hard and fast, and if I'm not ready to move to compliance, my reward will be a broken wrist.
If you think it looks fake, try to observe a class of Jiyu-waza or randori, where any attack can be met with any technique. This is a more free style, and the closest aikido gets to sparring. Watch black belts training with one another. Take a class and try and resist a 2nd dan or above aikidoka. Carefully.
check out a cool video: http://www.youtube.com/watch?v=fN7yn0XOSMQ
The criticism that aikido won't work against other martial arts is valid only if you allow those martial arts their strengths. I have a friend who's a boxer, he comes in close and tight, keeping his weight over his feet,and uses his fists like carronades, with short, powerful punches. I just stop him by putting my hand in his face. He either beats hell out of my arm, or he extends himself to overcome my reach, which then puts him in my world. Once I get his head from over the top of his hips, he's off balance, and he's mine.
Japanese police are restricted in their promotion opportunities until they master Aikido.
Aikido is a lot of fun, very challenging, and you meet the nicest people. The people who just want to learn a MA to beat up other people get frustrated very quickly and leave.