Starting a formula should not require "+", ""or "=" signs
In excel, when entering the first number in a formula, the entire string is treated as a text string unless a sign (+,  or =) is added at the beginning. Other mathematical software in the past gave priority to the number "value" in the cell instead of the text "value" and thus it was easier to do simple calculations and write formulas. For example: +5*5 yields 25 while 5*5 (without the sign) yields 5*5 (a text string). 5*5 shoul always yield 25 unless especified using '5*5, which already yields 5*5
4 comments

munira commented
infact users should be given an option to "tick" this feature that if you type 2 a "+"should auto complete the entry.

Anonymous commented
Amen

Ryan commented
I agree with Kenneth. Sometimes I want to write 5*5 and I want it to be a string.
I would get very frustrated if Excel interpreted 05 as a formula. I already get frustrated when it thinks 615 is June 15th. How would you enter the following data? You would have to use lots of single quotes.
Age ..........Cost of
Range ......Donkey Ride
05 ......... $2
615 ..........$10
1650 ....... $15
51+ ...........FREE 
Kenneth Barber commented
If you don't type in the =, then there's no way to easy way to signal to Excel that you are using a formula, so it cannot let you know if your formula is invalid. I suppose that it could still make a guess.
Also, even if = is no longer required to start a formula, I still think that it should be part of the final formula (automatically add it after pressing Enter). There is the odd time that you'll want the text of the formula (or the text of what looks like a formula) and not the formula itself. We don't want Excel to automatically and only interpret anything that looks like a formula as being a formula. That would lead to frustration similar to date interpretation:
https://excel.uservoice.com/forums/304921excelforwindowsdesktopapplication/suggestions/10108722allowustoturnoffautomaticconversiontodate