We use the suffix -ist to change a noun representing an object or activity into a noun representing a person who performs that activity. Since Paul McCartney is a person, he joined the group as a guitarist (a person who plays the guitar).

The word successful is an adjective. In English, we use adverbs (usually ending in -ly) to describe or modify adjectives. Commercially explains in what way they were successful—specifically regarding sales and profit.

This is a past participle used as an adjective. To be acclaimed means to be publicly praised or celebrated. When paired with critically, it describes how the band was viewed by professional music critics.

By adding the suffix -wide, we create an adjective that means extending throughout. Since their popularity reached across the entire globe (inferred from touring extensively), worldwide is suitable to describe that reach.

In this context, we need a noun to follow the definite article the. A break-up is a compound noun used specifically to describe the end of a relationship or of a group.

The base word depend is changed to the adverb independently (using the prefix in- for not and the suffix -ly). This describes how they found success: on their own, without the help of the other band members.

We need a noun to describe a physical location. While enter is a verb, entrance is the noun form that refers to the place where you go into a building.

The phrase some of their signals that we are comparing their music to everything else they created. We use the superlative form (finest) to show that this music was of the very highest quality.

This is a compound adjective used to describe a product that has sold in very large numbers. We use the superlative best combined with the present participle selling to indicate they are at the top of the list.

The prefix un- means not, and the suffix -ed turns it into an adjective. If something is unparalleled, it means it has no equal; nothing else is parallel or comparable to it.