You're always analyzing and critiquing. You can't help it - it's just the way you are! But is that ruining your first impression?
The people who know you are probably used to it and no doubt welcome (most of) your helpful suggestions. But if you're seeking a job, you might want to keep your opinions to yourself until asked.
Don't use a cover letter to detail the failings of the company's website or their latest marketing campaign. Would you tell a stranger how to cut her hair? OK, maybe you would, but if you want that job, land it first before you tell them how to improve things!